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 $191.91   6.283%   $203.9677   $203.97   $203.95   $204.00  
  Purchase #2 $33.92   6.854%   $36.2449   $36.24   $36.25   $36.20  
  Purchase #3 $12.60   11.161%   $14.0063   $14.01   $14.00   $14.00  
  Purchase #4 $57.68   7.251%   $61.8624   $61.86   $61.85   $61.90  
  Purchase #5 $248.31   6.193%   $263.6878   $263.69   $263.70   $263.70  
  Purchase #6 $248.56   11.286%   $276.6125   $276.61   $276.60   $276.60  
  Purchase #7 $242.82   9.383%   $265.6038   $265.60   $265.60   $265.60  
  7 purchase totals = $1,035.80       $1,121.9854   $1,121.98   $1,121.95   $1,122.00