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 $224.44   11.243%   $249.6738   $249.67   $249.65   $249.70  
  Purchase #2 $96.52   5.217%   $101.5554   $101.56   $101.55   $101.60  
  Purchase #3 $78.33   4.317%   $81.7115   $81.71   $81.70   $81.70  
  Purchase #4 $78.45   10.854%   $86.965   $86.97   $86.95   $87.00  
  Purchase #5 $209.28   11.560%   $233.4728   $233.47   $233.45   $233.50  
  Purchase #6 $213.54   12.762%   $240.792   $240.79   $240.80   $240.80  
  Purchase #7 $149.63   7.547%   $160.9226   $160.92   $160.90   $160.90  
  7 purchase totals = $1,050.19       $1,155.0931   $1,155.09   $1,155.00   $1,155.20