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 $94.76   12.674%   $106.7699   $106.77   $106.75   $106.80  
  Purchase #2 $204.93   5.482%   $216.1643   $216.16   $216.15   $216.20  
  Purchase #3 $68.53   4.320%   $71.4905   $71.49   $71.50   $71.50  
  Purchase #4 $116.32   13.847%   $132.4268   $132.43   $132.45   $132.40  
  Purchase #5 $30.62   10.386%   $33.8002   $33.80   $33.80   $33.80  
  Purchase #6 $124.40   6.474%   $132.4537   $132.45   $132.45   $132.50  
  Purchase #7 $202.63   4.778%   $212.3117   $212.31   $212.30   $212.30  
  7 purchase totals = $842.19       $905.4171   $905.41   $905.40   $905.50