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 $56.30   5.824%   $59.5789   $59.58   $59.60   $59.60  
  Purchase #2 $182.78   10.739%   $202.4087   $202.41   $202.40   $202.40  
  Purchase #3 $154.54   11.718%   $172.649   $172.65   $172.65   $172.60  
  Purchase #4 $13.63   10.437%   $15.0526   $15.05   $15.05   $15.10  
  Purchase #5 $113.51   6.799%   $121.2275   $121.23   $121.25   $121.20  
  Purchase #6 $180.34   9.719%   $197.8672   $197.87   $197.85   $197.90  
  Purchase #7 $201.79   13.461%   $228.953   $228.95   $228.95   $229.00  
  7 purchase totals = $902.89       $997.7369   $997.74   $997.75   $997.80