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 $236.38   4.819%   $247.7712   $247.77   $247.75   $247.80  
  Purchase #2 $194.77   4.554%   $203.6398   $203.64   $203.65   $203.60  
  Purchase #3 $220.88   11.852%   $247.0587   $247.06   $247.05   $247.10  
  Purchase #4 $245.26   12.220%   $275.2308   $275.23   $275.25   $275.20  
  Purchase #5 $19.28   11.745%   $21.5444   $21.54   $21.55   $21.50  
  Purchase #6 $60.40   3.462%   $62.491   $62.49   $62.50   $62.50  
  Purchase #7 $46.53   9.575%   $50.9852   $50.99   $51.00   $51.00  
  7 purchase totals = $1,023.50       $1,108.7211   $1,108.72   $1,108.75   $1,108.70