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 $94.58   12.665%   $106.5586   $106.56   $106.55   $106.60  
  Purchase #2 $84.41   10.484%   $93.2595   $93.26   $93.25   $93.30  
  Purchase #3 $167.77   12.622%   $188.9459   $188.95   $188.95   $188.90  
  Purchase #4 $37.87   10.566%   $41.8713   $41.87   $41.85   $41.90  
  Purchase #5 $33.48   7.686%   $36.0533   $36.05   $36.05   $36.10  
  Purchase #6 $216.89   6.479%   $230.9423   $230.94   $230.95   $230.90  
  Purchase #7 $135.87   13.598%   $154.3456   $154.35   $154.35   $154.30  
  7 purchase totals = $770.87       $851.9765   $851.98   $851.95   $852.00