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 $117.33   6.102%   $124.4895   $124.49   $124.50   $124.50  
  Purchase #2 $229.70   3.451%   $237.6269   $237.63   $237.65   $237.60  
  Purchase #3 $147.85   11.373%   $164.665   $164.67   $164.65   $164.70  
  Purchase #4 $51.39   9.856%   $56.455   $56.46   $56.45   $56.50  
  Purchase #5 $122.37   9.853%   $134.4271   $134.43   $134.45   $134.40  
  Purchase #6 $201.40   3.196%   $207.8367   $207.84   $207.85   $207.80  
  Purchase #7 $153.48   12.662%   $172.9136   $172.91   $172.90   $172.90  
  7 purchase totals = $1,023.52       $1,098.4138   $1,098.43   $1,098.45   $1,098.40