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 $85.47   13.218%   $96.7674   $96.77   $96.75   $96.80  
  Purchase #2 $34.62   3.686%   $35.8961   $35.90   $35.90   $35.90  
  Purchase #3 $55.79   8.658%   $60.6203   $60.62   $60.60   $60.60  
  Purchase #4 $174.96   8.215%   $189.333   $189.33   $189.35   $189.30  
  Purchase #5 $156.46   5.754%   $165.4627   $165.46   $165.45   $165.50  
  Purchase #6 $15.91   6.402%   $16.9286   $16.93   $16.95   $16.90  
  Purchase #7 $79.77   13.859%   $90.8253   $90.83   $90.85   $90.80  
  7 purchase totals = $602.98       $655.8334   $655.84   $655.85   $655.80