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 $108.57   4.332%   $113.2733   $113.27   $113.25   $113.30  
  Purchase #2 $61.39   12.324%   $68.9557   $68.96   $68.95   $69.00  
  Purchase #3 $155.45   10.367%   $171.5655   $171.57   $171.55   $171.60  
  Purchase #4 $81.27   13.358%   $92.126   $92.13   $92.15   $92.10  
  Purchase #5 $225.77   6.825%   $241.1788   $241.18   $241.20   $241.20  
  Purchase #6 $158.35   3.299%   $163.574   $163.57   $163.55   $163.60  
  Purchase #7 $203.68   8.632%   $221.2617   $221.26   $221.25   $221.30  
  7 purchase totals = $994.48       $1,071.9350   $1,071.94   $1,071.90   $1,072.10