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 $49.37   12.867%   $55.7224   $55.72   $55.70   $55.70  
  Purchase #2 $157.40   11.522%   $175.5356   $175.54   $175.55   $175.50  
  Purchase #3 $96.91   8.325%   $104.9778   $104.98   $105.00   $105.00  
  Purchase #4 $218.93   11.545%   $244.2055   $244.21   $244.20   $244.20  
  Purchase #5 $202.32   6.766%   $216.009   $216.01   $216.00   $216.00  
  Purchase #6 $244.38   9.626%   $267.904   $267.90   $267.90   $267.90  
  Purchase #7 $176.53   7.750%   $190.2111   $190.21   $190.20   $190.20  
  7 purchase totals = $1,145.84       $1,254.5654   $1,254.57   $1,254.55   $1,254.50