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 $10.62   3.813%   $11.0249   $11.02   $11.00   $11.00  
  Purchase #2 $70.51   4.399%   $73.6117   $73.61   $73.60   $73.60  
  Purchase #3 $25.43   11.749%   $28.4178   $28.42   $28.40   $28.40  
  Purchase #4 $107.47   9.111%   $117.2616   $117.26   $117.25   $117.30  
  Purchase #5 $132.38   8.476%   $143.6005   $143.60   $143.60   $143.60  
  Purchase #6 $240.58   4.803%   $252.1351   $252.14   $252.15   $252.10  
  Purchase #7 $240.37   10.332%   $265.205   $265.21   $265.20   $265.20  
  7 purchase totals = $827.36       $891.2566   $891.26   $891.20   $891.20