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 $76.81   9.599%   $84.183   $84.18   $84.20   $84.20  
  Purchase #2 $235.38   7.295%   $252.551   $252.55   $252.55   $252.60  
  Purchase #3 $53.93   11.497%   $60.1303   $60.13   $60.15   $60.10  
  Purchase #4 $172.41   7.240%   $184.8925   $184.89   $184.90   $184.90  
  Purchase #5 $62.66   4.499%   $65.4791   $65.48   $65.50   $65.50  
  Purchase #6 $218.90   5.605%   $231.1693   $231.17   $231.15   $231.20  
  Purchase #7 $107.79   10.138%   $118.7178   $118.72   $118.70   $118.70  
  7 purchase totals = $927.88       $997.1230   $997.12   $997.15   $997.20