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 $58.33   12.815%   $65.805   $65.81   $65.80   $65.80  
  Purchase #2 $162.78   4.658%   $170.3623   $170.36   $170.35   $170.40  
  Purchase #3 $24.83   6.824%   $26.5244   $26.52   $26.50   $26.50  
  Purchase #4 $185.98   5.678%   $196.5399   $196.54   $196.55   $196.50  
  Purchase #5 $124.67   4.762%   $130.6068   $130.61   $130.60   $130.60  
  Purchase #6 $204.40   9.305%   $223.4194   $223.42   $223.40   $223.40  
  Purchase #7 $185.34   4.504%   $193.6877   $193.69   $193.70   $193.70  
  7 purchase totals = $946.33       $1,006.9455   $1,006.95   $1,006.90   $1,006.90