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 $53.33   13.865%   $60.7242   $60.72   $60.70   $60.70  
  Purchase #2 $68.30   11.157%   $75.9202   $75.92   $75.90   $75.90  
  Purchase #3 $16.93   13.501%   $19.2157   $19.22   $19.20   $19.20  
  Purchase #4 $126.39   10.245%   $139.3387   $139.34   $139.35   $139.30  
  Purchase #5 $106.84   3.307%   $110.3732   $110.37   $110.35   $110.40  
  Purchase #6 $185.90   7.691%   $200.1976   $200.20   $200.20   $200.20  
  Purchase #7 $185.29   5.470%   $195.4254   $195.43   $195.45   $195.40  
  7 purchase totals = $742.98       $801.1950   $801.20   $801.15   $801.10