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 $239.70   9.681%   $262.9054   $262.91   $262.90   $262.90  
  Purchase #2 $84.32   11.309%   $93.8557   $93.86   $93.85   $93.90  
  Purchase #3 $48.92   7.837%   $52.7539   $52.75   $52.75   $52.80  
  Purchase #4 $156.64   12.691%   $176.5192   $176.52   $176.50   $176.50  
  Purchase #5 $229.69   10.834%   $254.5746   $254.57   $254.55   $254.60  
  Purchase #6 $112.49   6.202%   $119.4666   $119.47   $119.45   $119.50  
  Purchase #7 $16.49   6.378%   $17.5417   $17.54   $17.55   $17.50  
  7 purchase totals = $888.25       $977.6171   $977.62   $977.55   $977.70