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 $212.66   6.564%   $226.619   $226.62   $226.60   $226.60  
  Purchase #2 $57.89   6.143%   $61.4462   $61.45   $61.45   $61.40  
  Purchase #3 $114.75   3.535%   $118.8064   $118.81   $118.80   $118.80  
  Purchase #4 $12.56   5.709%   $13.2771   $13.28   $13.30   $13.30  
  Purchase #5 $230.54   11.329%   $256.6579   $256.66   $256.65   $256.70  
  Purchase #6 $249.26   5.327%   $262.5381   $262.54   $262.55   $262.50  
  Purchase #7 $8.75   8.589%   $9.5015   $9.50   $9.50   $9.50  
  7 purchase totals = $886.41       $948.8462   $948.86   $948.85   $948.80