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 $81.35   6.427%   $86.5784   $86.58   $86.60   $86.60  
  Purchase #2 $198.85   5.504%   $209.7947   $209.79   $209.80   $209.80  
  Purchase #3 $10.71   8.115%   $11.5791   $11.58   $11.60   $11.60  
  Purchase #4 $235.81   8.871%   $256.7287   $256.73   $256.75   $256.70  
  Purchase #5 $150.97   6.508%   $160.7951   $160.80   $160.80   $160.80  
  Purchase #6 $93.94   8.364%   $101.7971   $101.80   $101.80   $101.80  
  Purchase #7 $213.73   8.709%   $232.3437   $232.34   $232.35   $232.30  
  7 purchase totals = $985.36       $1,059.6168   $1,059.62   $1,059.70   $1,059.60