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 $141.64   4.841%   $148.4968   $148.50   $148.50   $148.50  
  Purchase #2 $138.87   4.219%   $144.7289   $144.73   $144.75   $144.70  
  Purchase #3 $54.53   13.587%   $61.939   $61.94   $61.95   $61.90  
  Purchase #4 $91.46   5.208%   $96.2232   $96.22   $96.20   $96.20  
  Purchase #5 $149.41   11.103%   $165.999   $166.00   $166.00   $166.00  
  Purchase #6 $195.71   9.849%   $214.9855   $214.99   $215.00   $215.00  
  Purchase #7 $179.35   11.384%   $199.7672   $199.77   $199.75   $199.80  
  7 purchase totals = $950.97       $1,032.1396   $1,032.15   $1,032.15   $1,032.10