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 $22.69   8.402%   $24.5964   $24.60   $24.60   $24.60  
  Purchase #2 $147.42   5.399%   $155.3792   $155.38   $155.40   $155.40  
  Purchase #3 $40.74   9.477%   $44.6009   $44.60   $44.60   $44.60  
  Purchase #4 $223.90   8.256%   $242.3852   $242.39   $242.40   $242.40  
  Purchase #5 $182.35   10.141%   $200.8421   $200.84   $200.85   $200.80  
  Purchase #6 $220.99   3.808%   $229.4053   $229.41   $229.40   $229.40  
  Purchase #7 $61.86   11.217%   $68.7988   $68.80   $68.80   $68.80  
  7 purchase totals = $899.95       $966.0079   $966.02   $966.05   $966.00