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 $194.85   4.195%   $203.024   $203.02   $203.00   $203.00  
  Purchase #2 $45.76   10.565%   $50.5945   $50.59   $50.60   $50.60  
  Purchase #3 $30.88   12.761%   $34.8206   $34.82   $34.80   $34.80  
  Purchase #4 $82.38   12.867%   $92.9798   $92.98   $93.00   $93.00  
  Purchase #5 $47.55   6.606%   $50.6912   $50.69   $50.70   $50.70  
  Purchase #6 $159.25   11.857%   $178.1323   $178.13   $178.15   $178.10  
  Purchase #7 $89.91   9.850%   $98.7661   $98.77   $98.75   $98.80  
  7 purchase totals = $650.58       $709.0085   $709.00   $709.00   $709.00