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 $231.86   13.448%   $263.0405   $263.04   $263.05   $263.00  
  Purchase #2 $104.51   7.222%   $112.0577   $112.06   $112.05   $112.10  
  Purchase #3 $40.49   11.623%   $45.1962   $45.20   $45.20   $45.20  
  Purchase #4 $212.74   5.585%   $224.6215   $224.62   $224.60   $224.60  
  Purchase #5 $221.30   13.833%   $251.9124   $251.91   $251.90   $251.90  
  Purchase #6 $144.70   4.553%   $151.2882   $151.29   $151.30   $151.30  
  Purchase #7 $210.44   7.164%   $225.5159   $225.52   $225.50   $225.50  
  7 purchase totals = $1,166.04       $1,273.6324   $1,273.64   $1,273.60   $1,273.60