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 $44.66   8.232%   $48.3364   $48.34   $48.35   $48.30  
  Purchase #2 $189.56   7.243%   $203.2898   $203.29   $203.30   $203.30  
  Purchase #3 $134.34   12.670%   $151.3609   $151.36   $151.35   $151.40  
  Purchase #4 $231.57   12.147%   $259.6988   $259.70   $259.70   $259.70  
  Purchase #5 $157.83   8.493%   $171.2345   $171.23   $171.25   $171.20  
  Purchase #6 $110.69   13.551%   $125.6896   $125.69   $125.70   $125.70  
  Purchase #7 $227.70   9.419%   $249.1471   $249.15   $249.15   $249.10  
  7 purchase totals = $1,096.35       $1,208.7571   $1,208.76   $1,208.80   $1,208.70