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 $55.50   7.291%   $59.5465   $59.55   $59.55   $59.50  
  Purchase #2 $187.48   7.206%   $200.9898   $200.99   $201.00   $201.00  
  Purchase #3 $93.50   7.272%   $100.2993   $100.30   $100.30   $100.30  
  Purchase #4 $83.27   4.813%   $87.2778   $87.28   $87.30   $87.30  
  Purchase #5 $10.32   8.208%   $11.1671   $11.17   $11.15   $11.20  
  Purchase #6 $62.52   5.629%   $66.0393   $66.04   $66.05   $66.00  
  Purchase #7 $133.43   3.282%   $137.8092   $137.81   $137.80   $137.80  
  7 purchase totals = $626.02       $663.1290   $663.14   $663.15   $663.10