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 $182.88   10.401%   $201.9013   $201.90   $201.90   $201.90  
  Purchase #2 $167.95   13.670%   $190.9088   $190.91   $190.90   $190.90  
  Purchase #3 $65.80   8.380%   $71.314   $71.31   $71.30   $71.30  
  Purchase #4 $240.50   8.564%   $261.0964   $261.10   $261.10   $261.10  
  Purchase #5 $199.80   5.802%   $211.3924   $211.39   $211.40   $211.40  
  Purchase #6 $170.60   11.147%   $189.6168   $189.62   $189.60   $189.60  
  Purchase #7 $117.88   12.250%   $132.3203   $132.32   $132.30   $132.30  
  7 purchase totals = $1,145.41       $1,258.5500   $1,258.55   $1,258.50   $1,258.50