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 $205.95   6.474%   $219.2832   $219.28   $219.30   $219.30  
  Purchase #2 $118.50   5.107%   $124.5518   $124.55   $124.55   $124.60  
  Purchase #3 $185.31   13.302%   $209.9599   $209.96   $209.95   $210.00  
  Purchase #4 $58.87   7.215%   $63.1175   $63.12   $63.10   $63.10  
  Purchase #5 $190.36   9.710%   $208.844   $208.84   $208.85   $208.80  
  Purchase #6 $26.50   8.512%   $28.7557   $28.76   $28.75   $28.80  
  Purchase #7 $39.51   4.207%   $41.1722   $41.17   $41.15   $41.20  
  7 purchase totals = $825.00       $895.6843   $895.68   $895.65   $895.80