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 $56.61   13.511%   $64.2586   $64.26   $64.25   $64.30  
  Purchase #2 $174.91   9.147%   $190.909   $190.91   $190.90   $190.90  
  Purchase #3 $131.92   8.678%   $143.368   $143.37   $143.35   $143.40  
  Purchase #4 $222.90   12.157%   $249.998   $250.00   $250.00   $250.00  
  Purchase #5 $204.29   10.382%   $225.4994   $225.50   $225.50   $225.50  
  Purchase #6 $95.87   6.117%   $101.7344   $101.73   $101.75   $101.70  
  Purchase #7 $212.48   5.329%   $223.8031   $223.80   $223.80   $223.80  
  7 purchase totals = $1,098.98       $1,199.5705   $1,199.57   $1,199.55   $1,199.60