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 $49.57   8.598%   $53.832   $53.83   $53.85   $53.80  
  Purchase #2 $240.25   3.386%   $248.3849   $248.38   $248.40   $248.40  
  Purchase #3 $215.64   11.393%   $240.2079   $240.21   $240.20   $240.20  
  Purchase #4 $96.25   6.688%   $102.6872   $102.69   $102.70   $102.70  
  Purchase #5 $180.96   13.264%   $204.9625   $204.96   $204.95   $205.00  
  Purchase #6 $113.84   3.795%   $118.1602   $118.16   $118.15   $118.20  
  Purchase #7 $97.66   10.557%   $107.97   $107.97   $107.95   $108.00  
  7 purchase totals = $994.17       $1,076.2047   $1,076.20   $1,076.20   $1,076.30