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 $241.71   10.709%   $267.5947   $267.59   $267.60   $267.60  
  Purchase #2 $204.62   9.535%   $224.1305   $224.13   $224.15   $224.10  
  Purchase #3 $45.66   6.306%   $48.5393   $48.54   $48.55   $48.50  
  Purchase #4 $97.93   7.571%   $105.3443   $105.34   $105.35   $105.30  
  Purchase #5 $241.86   4.492%   $252.7244   $252.72   $252.70   $252.70  
  Purchase #6 $219.41   5.151%   $230.7118   $230.71   $230.70   $230.70  
  Purchase #7 $72.50   10.862%   $80.375   $80.38   $80.40   $80.40  
  7 purchase totals = $1,123.69       $1,209.4200   $1,209.41   $1,209.45   $1,209.30