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 $235.87   6.262%   $250.6402   $250.64   $250.65   $250.60  
  Purchase #2 $119.92   13.423%   $136.0169   $136.02   $136.00   $136.00  
  Purchase #3 $193.27   9.111%   $210.8788   $210.88   $210.90   $210.90  
  Purchase #4 $231.98   11.380%   $258.3793   $258.38   $258.40   $258.40  
  Purchase #5 $83.86   10.679%   $92.8154   $92.82   $92.80   $92.80  
  Purchase #6 $146.46   5.506%   $154.5241   $154.52   $154.50   $154.50  
  Purchase #7 $155.65   7.807%   $167.8016   $167.80   $167.80   $167.80  
  7 purchase totals = $1,167.01       $1,271.0563   $1,271.06   $1,271.05   $1,271.00