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 $57.62   8.138%   $62.3091   $62.31   $62.30   $62.30  
  Purchase #2 $234.41   8.283%   $253.8262   $253.83   $253.85   $253.80  
  Purchase #3 $127.34   8.632%   $138.332   $138.33   $138.35   $138.30  
  Purchase #4 $207.57   12.746%   $234.0269   $234.03   $234.05   $234.00  
  Purchase #5 $26.42   9.234%   $28.8596   $28.86   $28.85   $28.90  
  Purchase #6 $119.60   3.202%   $123.4296   $123.43   $123.45   $123.40  
  Purchase #7 $246.28   5.801%   $260.5667   $260.57   $260.55   $260.60  
  7 purchase totals = $1,019.24       $1,101.3501   $1,101.36   $1,101.40   $1,101.30