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 $76.83   10.510%   $84.9048   $84.90   $84.90   $84.90  
  Purchase #2 $141.55   11.377%   $157.6541   $157.65   $157.65   $157.70  
  Purchase #3 $99.65   7.121%   $106.7461   $106.75   $106.75   $106.70  
  Purchase #4 $16.37   13.425%   $18.5677   $18.57   $18.55   $18.60  
  Purchase #5 $173.88   8.687%   $188.985   $188.99   $189.00   $189.00  
  Purchase #6 $246.91   13.811%   $281.0107   $281.01   $281.00   $281.00  
  Purchase #7 $154.25   5.517%   $162.76   $162.76   $162.75   $162.80  
  7 purchase totals = $909.44       $1,000.6284   $1,000.63   $1,000.60   $1,000.70