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 $55.38   13.108%   $62.6392   $62.64   $62.65   $62.60  
  Purchase #2 $65.74   4.265%   $68.5438   $68.54   $68.55   $68.50  
  Purchase #3 $72.67   10.812%   $80.5271   $80.53   $80.55   $80.50  
  Purchase #4 $217.51   5.650%   $229.7993   $229.80   $229.80   $229.80  
  Purchase #5 $59.74   9.108%   $65.1811   $65.18   $65.20   $65.20  
  Purchase #6 $174.88   10.249%   $192.8035   $192.80   $192.80   $192.80  
  Purchase #7 $223.44   8.621%   $242.7028   $242.70   $242.70   $242.70  
  7 purchase totals = $869.36       $942.1968   $942.19   $942.25   $942.10