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 $38.85   8.610%   $42.195   $42.20   $42.20   $42.20  
  Purchase #2 $232.52   9.287%   $254.1141   $254.11   $254.10   $254.10  
  Purchase #3 $59.64   13.579%   $67.7385   $67.74   $67.75   $67.70  
  Purchase #4 $221.42   5.281%   $233.1132   $233.11   $233.10   $233.10  
  Purchase #5 $74.58   7.562%   $80.2197   $80.22   $80.20   $80.20  
  Purchase #6 $202.28   6.274%   $214.971   $214.97   $214.95   $215.00  
  Purchase #7 $46.68   10.354%   $51.5132   $51.51   $51.50   $51.50  
  7 purchase totals = $875.97       $943.8647   $943.86   $943.80   $943.80