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 $60.25   13.735%   $68.5253   $68.53   $68.55   $68.50  
  Purchase #2 $209.90   9.771%   $230.4093   $230.41   $230.40   $230.40  
  Purchase #3 $164.81   8.587%   $178.9622   $178.96   $178.95   $179.00  
  Purchase #4 $79.38   9.740%   $87.1116   $87.11   $87.10   $87.10  
  Purchase #5 $87.85   8.191%   $95.0458   $95.05   $95.05   $95.00  
  Purchase #6 $91.37   7.593%   $98.3077   $98.31   $98.30   $98.30  
  Purchase #7 $172.55   12.246%   $193.6805   $193.68   $193.70   $193.70  
  7 purchase totals = $866.11       $952.0424   $952.05   $952.05   $952.00