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 $91.69   7.386%   $98.4622   $98.46   $98.45   $98.50  
  Purchase #2 $198.80   11.817%   $222.2922   $222.29   $222.30   $222.30  
  Purchase #3 $172.98   6.381%   $184.0179   $184.02   $184.00   $184.00  
  Purchase #4 $50.86   5.316%   $53.5637   $53.56   $53.55   $53.60  
  Purchase #5 $230.28   12.487%   $259.0351   $259.04   $259.05   $259.00  
  Purchase #6 $237.62   9.696%   $260.6596   $260.66   $260.65   $260.70  
  Purchase #7 $224.82   10.722%   $248.9252   $248.93   $248.95   $248.90  
  7 purchase totals = $1,207.05       $1,326.9559   $1,326.96   $1,326.95   $1,327.00