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 $238.98   11.625%   $266.7614   $266.76   $266.75   $266.80  
  Purchase #2 $131.51   10.421%   $145.2147   $145.21   $145.20   $145.20  
  Purchase #3 $120.85   5.497%   $127.4931   $127.49   $127.50   $127.50  
  Purchase #4 $228.34   4.110%   $237.7248   $237.72   $237.70   $237.70  
  Purchase #5 $99.46   6.689%   $106.1129   $106.11   $106.10   $106.10  
  Purchase #6 $249.35   11.519%   $278.0726   $278.07   $278.05   $278.10  
  Purchase #7 $179.35   3.296%   $185.2614   $185.26   $185.25   $185.30  
  7 purchase totals = $1,247.84       $1,346.6409   $1,346.62   $1,346.55   $1,346.70