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 $194.98   4.602%   $203.953   $203.95   $203.95   $204.00  
  Purchase #2 $131.81   4.342%   $137.5332   $137.53   $137.55   $137.50  
  Purchase #3 $91.54   9.153%   $99.9187   $99.92   $99.90   $99.90  
  Purchase #4 $230.64   3.491%   $238.6916   $238.69   $238.70   $238.70  
  Purchase #5 $124.97   3.252%   $129.034   $129.03   $129.05   $129.00  
  Purchase #6 $154.78   5.761%   $163.6969   $163.70   $163.70   $163.70  
  Purchase #7 $250.79   3.536%   $259.6579   $259.66   $259.65   $259.70  
  7 purchase totals = $1,179.51       $1,232.4853   $1,232.48   $1,232.50   $1,232.50