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 $208.86   3.185%   $215.5122   $215.51   $215.50   $215.50  
  Purchase #2 $194.68   13.244%   $220.4634   $220.46   $220.45   $220.50  
  Purchase #3 $161.97   5.316%   $170.5803   $170.58   $170.60   $170.60  
  Purchase #4 $119.95   6.103%   $127.2705   $127.27   $127.25   $127.30  
  Purchase #5 $98.78   13.843%   $112.4541   $112.45   $112.45   $112.50  
  Purchase #6 $7.40   7.609%   $7.9631   $7.96   $7.95   $8.00  
  Purchase #7 $235.97   4.747%   $247.1715   $247.17   $247.15   $247.20  
  7 purchase totals = $1,027.61       $1,101.4151   $1,101.40   $1,101.35   $1,101.60