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 $49.40   6.443%   $52.5828   $52.58   $52.60   $52.60  
  Purchase #2 $12.61   3.538%   $13.0561   $13.06   $13.05   $13.10  
  Purchase #3 $65.33   12.484%   $73.4858   $73.49   $73.50   $73.50  
  Purchase #4 $156.26   6.842%   $166.9513   $166.95   $166.95   $167.00  
  Purchase #5 $140.59   9.726%   $154.2638   $154.26   $154.25   $154.30  
  Purchase #6 $197.97   11.388%   $220.5148   $220.51   $220.50   $220.50  
  Purchase #7 $13.83   12.111%   $15.505   $15.51   $15.50   $15.50  
  7 purchase totals = $635.99       $696.3596   $696.36   $696.35   $696.50