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 $247.99   13.792%   $282.1928   $282.19   $282.20   $282.20  
  Purchase #2 $75.69   11.715%   $84.5571   $84.56   $84.55   $84.60  
  Purchase #3 $201.82   5.623%   $213.1683   $213.17   $213.15   $213.20  
  Purchase #4 $240.79   11.808%   $269.2225   $269.22   $269.20   $269.20  
  Purchase #5 $218.75   8.523%   $237.3941   $237.39   $237.40   $237.40  
  Purchase #6 $56.83   10.768%   $62.9495   $62.95   $62.95   $62.90  
  Purchase #7 $203.39   5.638%   $214.8571   $214.86   $214.85   $214.90  
  7 purchase totals = $1,245.26       $1,364.3414   $1,364.34   $1,364.30   $1,364.40