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 $84.50   12.657%   $95.1952   $95.20   $95.20   $95.20  
  Purchase #2 $58.78   9.757%   $64.5152   $64.52   $64.50   $64.50  
  Purchase #3 $71.44   11.616%   $79.7385   $79.74   $79.75   $79.70  
  Purchase #4 $189.47   8.679%   $205.9141   $205.91   $205.90   $205.90  
  Purchase #5 $18.90   3.627%   $19.5855   $19.59   $19.60   $19.60  
  Purchase #6 $241.37   4.658%   $252.613   $252.61   $252.60   $252.60  
  Purchase #7 $86.90   11.261%   $96.6858   $96.69   $96.70   $96.70  
  7 purchase totals = $751.36       $814.2473   $814.26   $814.25   $814.20