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 $202.87   13.639%   $230.5394   $230.54   $230.55   $230.50  
  Purchase #2 $193.78   12.593%   $218.1827   $218.18   $218.20   $218.20  
  Purchase #3 $5.64   5.802%   $5.9672   $5.97   $5.95   $6.00  
  Purchase #4 $230.89   5.404%   $243.3673   $243.37   $243.35   $243.40  
  Purchase #5 $208.79   3.215%   $215.5026   $215.50   $215.50   $215.50  
  Purchase #6 $195.33   13.471%   $221.6429   $221.64   $221.65   $221.60  
  Purchase #7 $122.29   10.399%   $135.0069   $135.01   $135.00   $135.00  
  7 purchase totals = $1,159.59       $1,270.2090   $1,270.21   $1,270.20   $1,270.20