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 $176.56   13.237%   $199.9312   $199.93   $199.95   $199.90  
  Purchase #2 $156.47   12.384%   $175.8472   $175.85   $175.85   $175.80  
  Purchase #3 $35.55   5.680%   $37.5692   $37.57   $37.55   $37.60  
  Purchase #4 $203.72   11.549%   $227.2476   $227.25   $227.25   $227.20  
  Purchase #5 $190.49   9.684%   $208.9371   $208.94   $208.95   $208.90  
  Purchase #6 $52.90   7.311%   $56.7675   $56.77   $56.75   $56.80  
  Purchase #7 $134.95   6.692%   $143.9809   $143.98   $144.00   $144.00  
  7 purchase totals = $950.64       $1,050.2807   $1,050.29   $1,050.30   $1,050.20