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 $218.87   10.312%   $241.4399   $241.44   $241.45   $241.40  
  Purchase #2 $134.36   9.209%   $146.7332   $146.73   $146.75   $146.70  
  Purchase #3 $63.60   6.804%   $67.9273   $67.93   $67.95   $67.90  
  Purchase #4 $14.92   5.303%   $15.7112   $15.71   $15.70   $15.70  
  Purchase #5 $243.84   13.573%   $276.9364   $276.94   $276.95   $276.90  
  Purchase #6 $32.97   4.823%   $34.5601   $34.56   $34.55   $34.60  
  Purchase #7 $243.95   10.268%   $268.9988   $269.00   $269.00   $269.00  
  7 purchase totals = $952.51       $1,052.3069   $1,052.31   $1,052.35   $1,052.20