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 $82.98   13.139%   $93.8827   $93.88   $93.90   $93.90  
  Purchase #2 $51.95   8.115%   $56.1657   $56.17   $56.15   $56.20  
  Purchase #3 $120.87   4.591%   $126.4191   $126.42   $126.40   $126.40  
  Purchase #4 $233.40   9.497%   $255.566   $255.57   $255.55   $255.60  
  Purchase #5 $87.72   7.186%   $94.0236   $94.02   $94.00   $94.00  
  Purchase #6 $96.78   10.557%   $106.9971   $107.00   $107.00   $107.00  
  Purchase #7 $195.93   3.558%   $202.9012   $202.90   $202.90   $202.90  
  7 purchase totals = $869.63       $935.9554   $935.96   $935.90   $936.00