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 $144.45   4.563%   $151.0413   $151.04   $151.05   $151.00  
  Purchase #2 $5.86   3.673%   $6.0752   $6.08   $6.10   $6.10  
  Purchase #3 $73.26   12.193%   $82.1926   $82.19   $82.20   $82.20  
  Purchase #4 $119.56   5.131%   $125.6946   $125.69   $125.70   $125.70  
  Purchase #5 $149.60   9.531%   $163.8584   $163.86   $163.85   $163.90  
  Purchase #6 $217.57   6.132%   $230.9114   $230.91   $230.90   $230.90  
  Purchase #7 $249.65   4.183%   $260.0929   $260.09   $260.10   $260.10  
  7 purchase totals = $959.95       $1,019.8664   $1,019.86   $1,019.90   $1,019.90