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 $105.71   5.314%   $111.3274   $111.33   $111.35   $111.30  
  Purchase #2 $213.44   12.362%   $239.8255   $239.83   $239.85   $239.80  
  Purchase #3 $26.42   9.855%   $29.0237   $29.02   $29.00   $29.00  
  Purchase #4 $213.77   5.210%   $224.9074   $224.91   $224.90   $224.90  
  Purchase #5 $89.82   3.517%   $92.979   $92.98   $93.00   $93.00  
  Purchase #6 $215.36   10.512%   $237.9986   $238.00   $238.00   $238.00  
  Purchase #7 $121.96   12.228%   $136.8733   $136.87   $136.85   $136.90  
  7 purchase totals = $986.48       $1,072.9349   $1,072.94   $1,072.95   $1,072.90