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 $65.46   13.463%   $74.2729   $74.27   $74.25   $74.30  
  Purchase #2 $59.32   12.321%   $66.6288   $66.63   $66.65   $66.60  
  Purchase #3 $131.65   11.851%   $147.2518   $147.25   $147.25   $147.30  
  Purchase #4 $92.48   4.213%   $96.3762   $96.38   $96.40   $96.40  
  Purchase #5 $111.77   6.577%   $119.1211   $119.12   $119.10   $119.10  
  Purchase #6 $21.28   4.474%   $22.2321   $22.23   $22.25   $22.20  
  Purchase #7 $35.74   7.279%   $38.3415   $38.34   $38.35   $38.30  
  7 purchase totals = $517.70       $564.2244   $564.22   $564.25   $564.20