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 $163.30   10.344%   $180.1918   $180.19   $180.20   $180.20  
  Purchase #2 $148.38   5.605%   $156.6967   $156.70   $156.70   $156.70  
  Purchase #3 $86.92   12.678%   $97.9397   $97.94   $97.95   $97.90  
  Purchase #4 $44.79   9.709%   $49.1387   $49.14   $49.15   $49.10  
  Purchase #5 $233.88   10.673%   $258.842   $258.84   $258.85   $258.80  
  Purchase #6 $204.48   13.726%   $232.5469   $232.55   $232.55   $232.50  
  Purchase #7 $7.76   9.182%   $8.4725   $8.47   $8.45   $8.50  
  7 purchase totals = $889.51       $983.8283   $983.83   $983.85   $983.70