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 $68.28   8.166%   $73.8557   $73.86   $73.85   $73.90  
  Purchase #2 $62.74   5.610%   $66.2597   $66.26   $66.25   $66.30  
  Purchase #3 $188.77   6.332%   $200.7229   $200.72   $200.70   $200.70  
  Purchase #4 $173.97   12.283%   $195.3387   $195.34   $195.35   $195.30  
  Purchase #5 $233.44   3.433%   $241.454   $241.45   $241.45   $241.50  
  Purchase #6 $216.91   10.743%   $240.2126   $240.21   $240.20   $240.20  
  Purchase #7 $52.63   7.155%   $56.3957   $56.40   $56.40   $56.40  
  7 purchase totals = $996.74       $1,074.2393   $1,074.24   $1,074.20   $1,074.30