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 $111.75   13.673%   $127.0296   $127.03   $127.05   $127.00  
  Purchase #2 $175.92   11.412%   $195.996   $196.00   $196.00   $196.00  
  Purchase #3 $101.29   10.868%   $112.2982   $112.30   $112.30   $112.30  
  Purchase #4 $247.71   8.477%   $268.7084   $268.71   $268.70   $268.70  
  Purchase #5 $234.80   6.133%   $249.2003   $249.20   $249.20   $249.20  
  Purchase #6 $84.46   10.828%   $93.6053   $93.61   $93.60   $93.60  
  Purchase #7 $201.95   9.255%   $220.6405   $220.64   $220.65   $220.60  
  7 purchase totals = $1,157.88       $1,267.4783   $1,267.49   $1,267.50   $1,267.40