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 $246.42   10.676%   $272.7278   $272.73   $272.75   $272.70  
  Purchase #2 $61.99   6.818%   $66.2165   $66.22   $66.20   $66.20  
  Purchase #3 $192.98   6.157%   $204.8618   $204.86   $204.85   $204.90  
  Purchase #4 $37.40   11.473%   $41.6909   $41.69   $41.70   $41.70  
  Purchase #5 $58.56   8.511%   $63.544   $63.54   $63.55   $63.50  
  Purchase #6 $182.73   7.244%   $195.967   $195.97   $195.95   $196.00  
  Purchase #7 $176.38   11.591%   $196.8242   $196.82   $196.80   $196.80  
  7 purchase totals = $956.46       $1,041.8322   $1,041.83   $1,041.80   $1,041.80