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 $109.91   3.211%   $113.4392   $113.44   $113.45   $113.40  
  Purchase #2 $190.81   5.149%   $200.6348   $200.63   $200.65   $200.60  
  Purchase #3 $118.42   3.675%   $122.7719   $122.77   $122.75   $122.80  
  Purchase #4 $30.31   6.228%   $32.1977   $32.20   $32.20   $32.20  
  Purchase #5 $104.44   12.559%   $117.5566   $117.56   $117.55   $117.60  
  Purchase #6 $245.87   8.278%   $266.2231   $266.22   $266.20   $266.20  
  Purchase #7 $203.81   6.120%   $216.2832   $216.28   $216.30   $216.30  
  7 purchase totals = $1,003.57       $1,069.1065   $1,069.10   $1,069.10   $1,069.10