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 $134.59   7.663%   $144.9036   $144.90   $144.90   $144.90  
  Purchase #2 $219.99   10.532%   $243.1593   $243.16   $243.15   $243.20  
  Purchase #3 $54.74   3.439%   $56.6225   $56.62   $56.60   $56.60  
  Purchase #4 $198.98   12.667%   $224.1848   $224.18   $224.20   $224.20  
  Purchase #5 $108.81   13.168%   $123.1381   $123.14   $123.15   $123.10  
  Purchase #6 $226.74   5.800%   $239.8909   $239.89   $239.90   $239.90  
  Purchase #7 $84.71   3.417%   $87.6045   $87.60   $87.60   $87.60  
  7 purchase totals = $1,028.56       $1,119.5037   $1,119.49   $1,119.50   $1,119.50