Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.84   12.561%   $244.0773   $244.08   $244.10   $244.10  
  Purchase #2 $144.98   10.839%   $160.6944   $160.69   $160.70   $160.70  
  Purchase #3 $240.29   12.167%   $269.5261   $269.53   $269.55   $269.50  
  Purchase #4 $110.63   13.302%   $125.346   $125.35   $125.35   $125.30  
  Purchase #5 $192.46   6.439%   $204.8525   $204.85   $204.85   $204.90  
  Purchase #6 $222.47   3.343%   $229.9072   $229.91   $229.90   $229.90  
  Purchase #7 $118.77   9.748%   $130.3477   $130.35   $130.35   $130.30  
  7 purchase totals = $1,246.44       $1,364.7512   $1,364.76   $1,364.80   $1,364.70