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 $103.86   13.859%   $118.254   $118.25   $118.25   $118.30  
  Purchase #2 $231.38   10.517%   $255.7142   $255.71   $255.70   $255.70  
  Purchase #3 $44.53   4.720%   $46.6318   $46.63   $46.65   $46.60  
  Purchase #4 $167.25   12.387%   $187.9673   $187.97   $187.95   $188.00  
  Purchase #5 $126.45   13.547%   $143.5802   $143.58   $143.60   $143.60  
  Purchase #6 $56.88   5.637%   $60.0863   $60.09   $60.10   $60.10  
  Purchase #7 $227.65   4.865%   $238.7252   $238.73   $238.75   $238.70  
  7 purchase totals = $958.00       $1,050.9590   $1,050.96   $1,051.00   $1,051.00