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 $238.51   12.762%   $268.9486   $268.95   $268.95   $268.90  
  Purchase #2 $193.86   5.852%   $205.2047   $205.20   $205.20   $205.20  
  Purchase #3 $146.64   12.662%   $165.2076   $165.21   $165.20   $165.20  
  Purchase #4 $10.48   13.161%   $11.8593   $11.86   $11.85   $11.90  
  Purchase #5 $120.25   12.323%   $135.0684   $135.07   $135.05   $135.10  
  Purchase #6 $90.85   12.186%   $101.921   $101.92   $101.90   $101.90  
  Purchase #7 $93.77   13.131%   $106.0829   $106.08   $106.10   $106.10  
  7 purchase totals = $894.36       $994.2925   $994.29   $994.25   $994.30