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 $76.43   5.832%   $80.8874   $80.89   $80.90   $80.90  
  Purchase #2 $214.38   9.731%   $235.2413   $235.24   $235.25   $235.20  
  Purchase #3 $8.44   10.487%   $9.3251   $9.33   $9.35   $9.30  
  Purchase #4 $176.60   5.140%   $185.6772   $185.68   $185.70   $185.70  
  Purchase #5 $53.47   11.627%   $59.687   $59.69   $59.70   $59.70  
  Purchase #6 $103.43   12.623%   $116.486   $116.49   $116.50   $116.50  
  Purchase #7 $183.49   9.334%   $200.617   $200.62   $200.60   $200.60  
  7 purchase totals = $816.24       $887.9210   $887.94   $888.00   $887.90