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 $65.84   11.164%   $73.1904   $73.19   $73.20   $73.20  
  Purchase #2 $209.97   12.252%   $235.6955   $235.70   $235.70   $235.70  
  Purchase #3 $25.66   7.477%   $27.5786   $27.58   $27.60   $27.60  
  Purchase #4 $221.81   11.754%   $247.8815   $247.88   $247.90   $247.90  
  Purchase #5 $95.70   5.859%   $101.3071   $101.31   $101.30   $101.30  
  Purchase #6 $106.34   11.628%   $118.7052   $118.71   $118.70   $118.70  
  Purchase #7 $70.71   13.140%   $80.0013   $80.00   $80.00   $80.00  
  7 purchase totals = $796.03       $884.3596   $884.37   $884.40   $884.40