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 $227.84   11.221%   $253.4059   $253.41   $253.40   $253.40  
  Purchase #2 $70.41   13.237%   $79.7302   $79.73   $79.75   $79.70  
  Purchase #3 $116.48   8.817%   $126.75   $126.75   $126.75   $126.80  
  Purchase #4 $54.33   5.428%   $57.279   $57.28   $57.30   $57.30  
  Purchase #5 $227.83   9.689%   $249.9044   $249.90   $249.90   $249.90  
  Purchase #6 $96.96   13.444%   $109.9953   $110.00   $110.00   $110.00  
  Purchase #7 $197.54   11.804%   $220.8576   $220.86   $220.85   $220.90  
  7 purchase totals = $991.39       $1,097.9224   $1,097.93   $1,097.95   $1,098.00