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 $214.62   5.295%   $225.9841   $225.98   $226.00   $226.00  
  Purchase #2 $69.94   10.813%   $77.5026   $77.50   $77.50   $77.50  
  Purchase #3 $97.55   5.318%   $102.7377   $102.74   $102.75   $102.70  
  Purchase #4 $81.98   7.150%   $87.8416   $87.84   $87.85   $87.80  
  Purchase #5 $191.29   11.543%   $213.3706   $213.37   $213.35   $213.40  
  Purchase #6 $154.95   12.264%   $173.9531   $173.95   $173.95   $174.00  
  Purchase #7 $51.68   3.730%   $53.6077   $53.61   $53.60   $53.60  
  7 purchase totals = $862.01       $934.9974   $934.99   $935.00   $935.00