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 $22.73   6.487%   $24.2045   $24.20   $24.20   $24.20  
  Purchase #2 $106.53   3.709%   $110.4812   $110.48   $110.50   $110.50  
  Purchase #3 $152.74   13.221%   $172.9338   $172.93   $172.95   $172.90  
  Purchase #4 $134.27   7.802%   $144.7457   $144.75   $144.75   $144.70  
  Purchase #5 $83.94   3.205%   $86.6303   $86.63   $86.65   $86.60  
  Purchase #6 $179.64   11.120%   $199.616   $199.62   $199.60   $199.60  
  Purchase #7 $21.42   9.479%   $23.4504   $23.45   $23.45   $23.50  
  7 purchase totals = $701.27       $762.0619   $762.06   $762.10   $762.00