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 $23.36   11.307%   $26.0013   $26.00   $26.00   $26.00  
  Purchase #2 $56.57   5.819%   $59.8618   $59.86   $59.85   $59.90  
  Purchase #3 $231.35   12.785%   $260.9281   $260.93   $260.95   $260.90  
  Purchase #4 $82.94   13.279%   $93.9536   $93.95   $93.95   $94.00  
  Purchase #5 $94.70   5.692%   $100.0903   $100.09   $100.10   $100.10  
  Purchase #6 $121.47   7.262%   $130.2912   $130.29   $130.30   $130.30  
  Purchase #7 $249.92   9.280%   $273.1126   $273.11   $273.10   $273.10  
  7 purchase totals = $860.31       $944.2389   $944.23   $944.25   $944.30