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 $154.61   8.182%   $167.2602   $167.26   $167.25   $167.30  
  Purchase #2 $10.98   4.247%   $11.4463   $11.45   $11.45   $11.40  
  Purchase #3 $93.27   7.350%   $100.1253   $100.13   $100.15   $100.10  
  Purchase #4 $55.59   13.855%   $63.292   $63.29   $63.30   $63.30  
  Purchase #5 $33.57   4.230%   $34.99   $34.99   $35.00   $35.00  
  Purchase #6 $106.55   11.287%   $118.5763   $118.58   $118.60   $118.60  
  Purchase #7 $137.44   10.121%   $151.3503   $151.35   $151.35   $151.40  
  7 purchase totals = $592.01       $647.0404   $647.05   $647.10   $647.10