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 $219.48   11.260%   $244.1934   $244.19   $244.20   $244.20  
  Purchase #2 $161.51   4.594%   $168.9298   $168.93   $168.95   $168.90  
  Purchase #3 $93.60   3.549%   $96.9219   $96.92   $96.90   $96.90  
  Purchase #4 $123.65   3.815%   $128.3672   $128.37   $128.35   $128.40  
  Purchase #5 $224.99   9.451%   $246.2538   $246.25   $246.25   $246.30  
  Purchase #6 $118.54   4.533%   $123.9134   $123.91   $123.90   $123.90  
  Purchase #7 $249.79   6.630%   $266.3511   $266.35   $266.35   $266.40  
  7 purchase totals = $1,191.56       $1,274.9306   $1,274.92   $1,274.90   $1,275.00