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 $223.95   13.711%   $254.6558   $254.66   $254.65   $254.70  
  Purchase #2 $243.26   10.309%   $268.3377   $268.34   $268.35   $268.30  
  Purchase #3 $229.61   7.854%   $247.6436   $247.64   $247.65   $247.60  
  Purchase #4 $213.62   10.729%   $236.5393   $236.54   $236.55   $236.50  
  Purchase #5 $177.57   11.422%   $197.852   $197.85   $197.85   $197.90  
  Purchase #6 $30.48   12.188%   $34.1949   $34.19   $34.20   $34.20  
  Purchase #7 $149.86   3.626%   $155.2939   $155.29   $155.30   $155.30  
  7 purchase totals = $1,268.35       $1,394.5172   $1,394.51   $1,394.55   $1,394.50