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 $93.81   5.463%   $98.9348   $98.93   $98.95   $98.90  
  Purchase #2 $193.99   12.336%   $217.9206   $217.92   $217.90   $217.90  
  Purchase #3 $191.91   6.781%   $204.9234   $204.92   $204.90   $204.90  
  Purchase #4 $235.74   13.466%   $267.4847   $267.48   $267.50   $267.50  
  Purchase #5 $54.50   13.608%   $61.9164   $61.92   $61.90   $61.90  
  Purchase #6 $173.85   7.519%   $186.9218   $186.92   $186.90   $186.90  
  Purchase #7 $15.73   4.700%   $16.4693   $16.47   $16.45   $16.50  
  7 purchase totals = $959.53       $1,054.5710   $1,054.56   $1,054.50   $1,054.50