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 $59.78   10.536%   $66.0784   $66.08   $66.10   $66.10  
  Purchase #2 $91.76   5.457%   $96.7673   $96.77   $96.75   $96.80  
  Purchase #3 $176.73   8.491%   $191.7361   $191.74   $191.75   $191.70  
  Purchase #4 $235.98   5.590%   $249.1713   $249.17   $249.15   $249.20  
  Purchase #5 $182.98   10.284%   $201.7977   $201.80   $201.80   $201.80  
  Purchase #6 $218.98   13.267%   $248.0321   $248.03   $248.05   $248.00  
  Purchase #7 $194.63   6.345%   $206.9793   $206.98   $207.00   $207.00  
  7 purchase totals = $1,160.84       $1,260.5622   $1,260.57   $1,260.60   $1,260.60