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 $183.40   12.738%   $206.7615   $206.76   $206.75   $206.80  
  Purchase #2 $208.81   4.329%   $217.8494   $217.85   $217.85   $217.80  
  Purchase #3 $37.88   12.487%   $42.6101   $42.61   $42.60   $42.60  
  Purchase #4 $194.34   4.559%   $203.2   $203.20   $203.20   $203.20  
  Purchase #5 $8.25   6.397%   $8.7778   $8.78   $8.80   $8.80  
  Purchase #6 $14.35   11.831%   $16.0477   $16.05   $16.05   $16.00  
  Purchase #7 $49.94   4.818%   $52.3461   $52.35   $52.35   $52.30  
  7 purchase totals = $696.97       $747.5926   $747.60   $747.60   $747.50