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 $142.89   9.143%   $155.9544   $155.95   $155.95   $156.00  
  Purchase #2 $110.83   10.381%   $122.3353   $122.34   $122.35   $122.30  
  Purchase #3 $208.66   3.413%   $215.7816   $215.78   $215.80   $215.80  
  Purchase #4 $185.98   8.171%   $201.1764   $201.18   $201.20   $201.20  
  Purchase #5 $6.73   8.306%   $7.289   $7.29   $7.30   $7.30  
  Purchase #6 $123.45   5.283%   $129.9719   $129.97   $129.95   $130.00  
  Purchase #7 $174.25   11.533%   $194.3463   $194.35   $194.35   $194.30  
  7 purchase totals = $952.79       $1,026.8549   $1,026.86   $1,026.90   $1,026.90