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 $186.88   12.111%   $209.513   $209.51   $209.50   $209.50  
  Purchase #2 $83.96   11.594%   $93.6943   $93.69   $93.70   $93.70  
  Purchase #3 $10.82   13.855%   $12.3191   $12.32   $12.30   $12.30  
  Purchase #4 $56.44   7.440%   $60.6391   $60.64   $60.65   $60.60  
  Purchase #5 $227.53   5.569%   $240.2011   $240.20   $240.20   $240.20  
  Purchase #6 $157.92   4.145%   $164.4658   $164.47   $164.45   $164.50  
  Purchase #7 $239.59   7.679%   $257.9881   $257.99   $258.00   $258.00  
  7 purchase totals = $963.14       $1,038.8205   $1,038.82   $1,038.80   $1,038.80