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 $48.77   11.139%   $54.2025   $54.20   $54.20   $54.20  
  Purchase #2 $77.71   13.598%   $88.277   $88.28   $88.30   $88.30  
  Purchase #3 $10.35   11.207%   $11.5099   $11.51   $11.50   $11.50  
  Purchase #4 $31.72   11.443%   $35.3497   $35.35   $35.35   $35.30  
  Purchase #5 $180.89   7.641%   $194.7118   $194.71   $194.70   $194.70  
  Purchase #6 $91.92   9.503%   $100.6552   $100.66   $100.65   $100.70  
  Purchase #7 $240.96   4.693%   $252.2683   $252.27   $252.25   $252.30  
  7 purchase totals = $682.32       $736.9744   $736.98   $736.95   $737.00