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 $206.98   12.500%   $232.8525   $232.85   $232.85   $232.90  
  Purchase #2 $23.95   8.455%   $25.975   $25.98   $26.00   $26.00  
  Purchase #3 $226.97   6.783%   $242.3654   $242.37   $242.35   $242.40  
  Purchase #4 $136.40   3.806%   $141.5914   $141.59   $141.60   $141.60  
  Purchase #5 $95.31   11.213%   $105.9971   $106.00   $106.00   $106.00  
  Purchase #6 $7.58   13.153%   $8.577   $8.58   $8.60   $8.60  
  Purchase #7 $232.99   10.264%   $256.9041   $256.90   $256.90   $256.90  
  7 purchase totals = $930.18       $1,014.2625   $1,014.27   $1,014.30   $1,014.40