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 $90.41   6.224%   $96.0371   $96.04   $96.05   $96.00  
  Purchase #2 $242.96   10.648%   $268.8304   $268.83   $268.85   $268.80  
  Purchase #3 $177.70   10.235%   $195.8876   $195.89   $195.90   $195.90  
  Purchase #4 $32.50   8.266%   $35.1865   $35.19   $35.20   $35.20  
  Purchase #5 $55.45   4.683%   $58.0467   $58.05   $58.05   $58.00  
  Purchase #6 $146.61   10.744%   $162.3618   $162.36   $162.35   $162.40  
  Purchase #7 $148.28   10.400%   $163.7011   $163.70   $163.70   $163.70  
  7 purchase totals = $893.91       $980.0512   $980.06   $980.10   $980.00