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 $57.94   6.573%   $61.7484   $61.75   $61.75   $61.70  
  Purchase #2 $149.66   4.530%   $156.4396   $156.44   $156.45   $156.40  
  Purchase #3 $41.54   3.489%   $42.9893   $42.99   $43.00   $43.00  
  Purchase #4 $53.70   7.756%   $57.865   $57.87   $57.85   $57.90  
  Purchase #5 $182.53   6.151%   $193.7574   $193.76   $193.75   $193.80  
  Purchase #6 $169.47   3.764%   $175.8489   $175.85   $175.85   $175.80  
  Purchase #7 $138.96   5.587%   $146.7237   $146.72   $146.70   $146.70  
  7 purchase totals = $793.80       $835.3723   $835.38   $835.35   $835.30