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 $35.33   6.663%   $37.684   $37.68   $37.70   $37.70  
  Purchase #2 $107.37   8.613%   $116.6178   $116.62   $116.60   $116.60  
  Purchase #3 $141.84   13.640%   $161.187   $161.19   $161.20   $161.20  
  Purchase #4 $190.99   6.130%   $202.6977   $202.70   $202.70   $202.70  
  Purchase #5 $194.76   11.391%   $216.9451   $216.95   $216.95   $216.90  
  Purchase #6 $106.32   10.214%   $117.1795   $117.18   $117.20   $117.20  
  Purchase #7 $55.92   6.721%   $59.6784   $59.68   $59.70   $59.70  
  7 purchase totals = $832.53       $911.9895   $912.00   $912.05   $912.00