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 $233.75   11.790%   $261.3091   $261.31   $261.30   $261.30  
  Purchase #2 $63.68   3.794%   $66.096   $66.10   $66.10   $66.10  
  Purchase #3 $135.51   5.501%   $142.9644   $142.96   $142.95   $143.00  
  Purchase #4 $72.48   4.633%   $75.838   $75.84   $75.85   $75.80  
  Purchase #5 $238.42   11.732%   $266.3914   $266.39   $266.40   $266.40  
  Purchase #6 $151.50   10.841%   $167.9241   $167.92   $167.90   $167.90  
  Purchase #7 $155.65   5.631%   $164.4147   $164.41   $164.40   $164.40  
  7 purchase totals = $1,050.99       $1,144.9377   $1,144.93   $1,144.90   $1,144.90