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 $116.84   7.257%   $125.3191   $125.32   $125.30   $125.30  
  Purchase #2 $67.82   11.754%   $75.7916   $75.79   $75.80   $75.80  
  Purchase #3 $158.35   5.355%   $166.8296   $166.83   $166.85   $166.80  
  Purchase #4 $203.70   5.468%   $214.8383   $214.84   $214.85   $214.80  
  Purchase #5 $225.93   4.471%   $236.0313   $236.03   $236.05   $236.00  
  Purchase #6 $41.28   10.135%   $45.4637   $45.46   $45.45   $45.50  
  Purchase #7 $139.28   7.443%   $149.6466   $149.65   $149.65   $149.60  
  7 purchase totals = $953.20       $1,013.9202   $1,013.92   $1,013.95   $1,013.80