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 $230.82   6.677%   $246.2319   $246.23   $246.25   $246.20  
  Purchase #2 $184.74   3.505%   $191.2151   $191.22   $191.20   $191.20  
  Purchase #3 $209.62   6.163%   $222.5389   $222.54   $222.55   $222.50  
  Purchase #4 $154.28   13.796%   $175.5645   $175.56   $175.55   $175.60  
  Purchase #5 $123.36   9.696%   $135.321   $135.32   $135.30   $135.30  
  Purchase #6 $229.32   8.271%   $248.2871   $248.29   $248.30   $248.30  
  Purchase #7 $59.94   5.283%   $63.1066   $63.11   $63.10   $63.10  
  7 purchase totals = $1,192.08       $1,282.2651   $1,282.27   $1,282.25   $1,282.20