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 $116.90   8.460%   $126.7897   $126.79   $126.80   $126.80  
  Purchase #2 $210.60   11.186%   $234.1577   $234.16   $234.15   $234.20  
  Purchase #3 $5.55   12.230%   $6.2288   $6.23   $6.25   $6.20  
  Purchase #4 $197.54   5.634%   $208.6694   $208.67   $208.65   $208.70  
  Purchase #5 $160.69   8.599%   $174.5077   $174.51   $174.50   $174.50  
  Purchase #6 $13.39   11.519%   $14.9324   $14.93   $14.95   $14.90  
  Purchase #7 $16.64   6.330%   $17.6933   $17.69   $17.70   $17.70  
  7 purchase totals = $721.31       $782.9790   $782.98   $783.00   $783.00