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 $104.85   10.276%   $115.6244   $115.62   $115.60   $115.60  
  Purchase #2 $221.98   13.227%   $251.3413   $251.34   $251.35   $251.30  
  Purchase #3 $127.51   7.460%   $137.0222   $137.02   $137.00   $137.00  
  Purchase #4 $144.65   9.822%   $158.8575   $158.86   $158.85   $158.90  
  Purchase #5 $250.74   7.274%   $268.9788   $268.98   $269.00   $269.00  
  Purchase #6 $250.58   11.847%   $280.2662   $280.27   $280.25   $280.30  
  Purchase #7 $207.64   13.154%   $234.953   $234.95   $234.95   $235.00  
  7 purchase totals = $1,307.95       $1,447.0434   $1,447.04   $1,447.00   $1,447.10