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 $25.96   6.361%   $27.6113   $27.61   $27.60   $27.60  
  Purchase #2 $162.82   7.258%   $174.6375   $174.64   $174.65   $174.60  
  Purchase #3 $107.76   7.793%   $116.1577   $116.16   $116.15   $116.20  
  Purchase #4 $230.31   13.779%   $262.0444   $262.04   $262.05   $262.00  
  Purchase #5 $91.84   13.577%   $104.3091   $104.31   $104.30   $104.30  
  Purchase #6 $119.77   13.258%   $135.6491   $135.65   $135.65   $135.60  
  Purchase #7 $189.95   13.193%   $215.0101   $215.01   $215.00   $215.00  
  7 purchase totals = $928.41       $1,035.4192   $1,035.42   $1,035.40   $1,035.30