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 $245.75   12.319%   $276.0239   $276.02   $276.00   $276.00  
  Purchase #2 $221.38   5.789%   $234.1957   $234.20   $234.20   $234.20  
  Purchase #3 $245.74   5.287%   $258.7323   $258.73   $258.75   $258.70  
  Purchase #4 $237.41   7.525%   $255.2751   $255.28   $255.30   $255.30  
  Purchase #5 $64.98   13.152%   $73.5262   $73.53   $73.55   $73.50  
  Purchase #6 $178.68   10.390%   $197.2449   $197.24   $197.25   $197.20  
  Purchase #7 $7.31   3.112%   $7.5375   $7.54   $7.55   $7.50  
  7 purchase totals = $1,201.25       $1,302.5356   $1,302.54   $1,302.60   $1,302.40