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 $74.66   12.325%   $83.8618   $83.86   $83.85   $83.90  
  Purchase #2 $208.56   11.375%   $232.2837   $232.28   $232.30   $232.30  
  Purchase #3 $72.42   5.500%   $76.4031   $76.40   $76.40   $76.40  
  Purchase #4 $148.44   12.728%   $167.3334   $167.33   $167.35   $167.30  
  Purchase #5 $148.53   9.667%   $162.8884   $162.89   $162.90   $162.90  
  Purchase #6 $206.75   12.210%   $231.9942   $231.99   $232.00   $232.00  
  Purchase #7 $161.43   7.778%   $173.986   $173.99   $174.00   $174.00  
  7 purchase totals = $1,020.79       $1,128.7506   $1,128.74   $1,128.80   $1,128.80