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 $127.33   6.824%   $136.019   $136.02   $136.00   $136.00  
  Purchase #2 $189.30   6.614%   $201.8203   $201.82   $201.80   $201.80  
  Purchase #3 $142.68   4.609%   $149.2561   $149.26   $149.25   $149.30  
  Purchase #4 $169.49   5.168%   $178.2492   $178.25   $178.25   $178.20  
  Purchase #5 $27.52   8.285%   $29.8   $29.80   $29.80   $29.80  
  Purchase #6 $12.97   4.766%   $13.5882   $13.59   $13.60   $13.60  
  Purchase #7 $154.27   6.207%   $163.8455   $163.85   $163.85   $163.80  
  7 purchase totals = $823.56       $872.5783   $872.59   $872.55   $872.50