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 $120.30   11.601%   $134.256   $134.26   $134.25   $134.30  
  Purchase #2 $198.84   5.457%   $209.6907   $209.69   $209.70   $209.70  
  Purchase #3 $161.41   8.383%   $174.941   $174.94   $174.95   $174.90  
  Purchase #4 $159.41   7.186%   $170.8652   $170.87   $170.85   $170.90  
  Purchase #5 $9.95   7.204%   $10.6668   $10.67   $10.65   $10.70  
  Purchase #6 $118.93   13.711%   $135.2365   $135.24   $135.25   $135.20  
  Purchase #7 $86.84   9.729%   $95.2887   $95.29   $95.30   $95.30  
  7 purchase totals = $855.68       $930.9449   $930.96   $930.95   $931.00