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 $47.95   7.582%   $51.5856   $51.59   $51.60   $51.60  
  Purchase #2 $244.25   12.373%   $274.4711   $274.47   $274.45   $274.50  
  Purchase #3 $31.28   9.518%   $34.2572   $34.26   $34.25   $34.30  
  Purchase #4 $213.36   12.759%   $240.5826   $240.58   $240.60   $240.60  
  Purchase #5 $68.33   11.167%   $75.9604   $75.96   $75.95   $76.00  
  Purchase #6 $19.70   8.310%   $21.3371   $21.34   $21.35   $21.30  
  Purchase #7 $134.65   12.153%   $151.014   $151.01   $151.00   $151.00  
  7 purchase totals = $759.52       $849.2080   $849.21   $849.20   $849.30