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 $61.37   12.412%   $68.9872   $68.99   $69.00   $69.00  
  Purchase #2 $206.32   12.553%   $232.2193   $232.22   $232.20   $232.20  
  Purchase #3 $130.47   9.635%   $143.0408   $143.04   $143.05   $143.00  
  Purchase #4 $125.27   8.460%   $135.8678   $135.87   $135.85   $135.90  
  Purchase #5 $14.45   11.619%   $16.1289   $16.13   $16.15   $16.10  
  Purchase #6 $161.52   6.749%   $172.421   $172.42   $172.40   $172.40  
  Purchase #7 $24.91   5.388%   $26.2522   $26.25   $26.25   $26.30  
  7 purchase totals = $724.31       $794.9172   $794.92   $794.90   $794.90