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 $108.51   5.561%   $114.5442   $114.54   $114.55   $114.50  
  Purchase #2 $236.67   7.729%   $254.9622   $254.96   $254.95   $255.00  
  Purchase #3 $103.38   7.367%   $110.996   $111.00   $111.00   $111.00  
  Purchase #4 $135.45   9.641%   $148.5087   $148.51   $148.50   $148.50  
  Purchase #5 $93.72   13.261%   $106.1482   $106.15   $106.15   $106.10  
  Purchase #6 $154.44   8.331%   $167.3064   $167.31   $167.30   $167.30  
  Purchase #7 $29.30   4.759%   $30.6944   $30.69   $30.70   $30.70  
  7 purchase totals = $861.47       $933.1601   $933.16   $933.15   $933.10