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 $77.28   12.158%   $86.6757   $86.68   $86.70   $86.70  
  Purchase #2 $55.88   11.538%   $62.3274   $62.33   $62.35   $62.30  
  Purchase #3 $238.43   6.229%   $253.2818   $253.28   $253.30   $253.30  
  Purchase #4 $97.99   6.769%   $104.6229   $104.62   $104.60   $104.60  
  Purchase #5 $116.82   7.179%   $125.2065   $125.21   $125.20   $125.20  
  Purchase #6 $205.46   6.751%   $219.3306   $219.33   $219.35   $219.30  
  Purchase #7 $160.84   5.810%   $170.1848   $170.18   $170.20   $170.20  
  7 purchase totals = $952.70       $1,021.6297   $1,021.63   $1,021.70   $1,021.60