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 $87.84   5.648%   $92.8012   $92.80   $92.80   $92.80  
  Purchase #2 $123.87   5.842%   $131.1065   $131.11   $131.10   $131.10  
  Purchase #3 $18.95   11.322%   $21.0955   $21.10   $21.10   $21.10  
  Purchase #4 $238.93   9.842%   $262.4455   $262.45   $262.45   $262.40  
  Purchase #5 $83.51   5.705%   $88.2742   $88.27   $88.25   $88.30  
  Purchase #6 $206.82   9.754%   $226.9932   $226.99   $227.00   $227.00  
  Purchase #7 $123.94   8.131%   $134.0176   $134.02   $134.00   $134.00  
  7 purchase totals = $883.86       $956.7337   $956.74   $956.70   $956.70