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 $45.84   12.604%   $51.6177   $51.62   $51.60   $51.60  
  Purchase #2 $219.29   9.431%   $239.9712   $239.97   $239.95   $240.00  
  Purchase #3 $19.49   8.113%   $21.0712   $21.07   $21.05   $21.10  
  Purchase #4 $63.95   4.814%   $67.0286   $67.03   $67.05   $67.00  
  Purchase #5 $187.56   6.210%   $199.2075   $199.21   $199.20   $199.20  
  Purchase #6 $33.42   9.182%   $36.4886   $36.49   $36.50   $36.50  
  Purchase #7 $223.40   13.247%   $252.9938   $252.99   $253.00   $253.00  
  7 purchase totals = $792.95       $868.3786   $868.38   $868.35   $868.40