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 $119.66   13.233%   $135.4946   $135.49   $135.50   $135.50  
  Purchase #2 $91.96   6.499%   $97.9365   $97.94   $97.95   $97.90  
  Purchase #3 $167.81   7.306%   $180.0702   $180.07   $180.05   $180.10  
  Purchase #4 $173.83   6.194%   $184.597   $184.60   $184.60   $184.60  
  Purchase #5 $90.93   11.855%   $101.7098   $101.71   $101.70   $101.70  
  Purchase #6 $76.84   8.240%   $83.1716   $83.17   $83.15   $83.20  
  Purchase #7 $245.46   9.582%   $268.98   $268.98   $269.00   $269.00  
  7 purchase totals = $966.49       $1,051.9597   $1,051.96   $1,051.95   $1,052.00