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 $246.83   10.336%   $272.3423   $272.34   $272.35   $272.30  
  Purchase #2 $167.55   9.177%   $182.9261   $182.93   $182.95   $182.90  
  Purchase #3 $168.30   6.331%   $178.9551   $178.96   $178.95   $179.00  
  Purchase #4 $67.42   3.261%   $69.6186   $69.62   $69.60   $69.60  
  Purchase #5 $152.57   13.604%   $173.3256   $173.33   $173.35   $173.30  
  Purchase #6 $171.90   6.619%   $183.2781   $183.28   $183.30   $183.30  
  Purchase #7 $52.43   13.535%   $59.5264   $59.53   $59.55   $59.50  
  7 purchase totals = $1,027.00       $1,119.9722   $1,119.99   $1,120.05   $1,119.90