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 $9.64   3.617%   $9.9887   $9.99   $10.00   $10.00  
  Purchase #2 $143.87   12.384%   $161.6869   $161.69   $161.70   $161.70  
  Purchase #3 $23.25   9.863%   $25.5431   $25.54   $25.55   $25.50  
  Purchase #4 $113.49   10.630%   $125.554   $125.55   $125.55   $125.60  
  Purchase #5 $48.78   10.170%   $53.7409   $53.74   $53.75   $53.70  
  Purchase #6 $62.93   3.512%   $65.1401   $65.14   $65.15   $65.10  
  Purchase #7 $231.33   9.290%   $252.8206   $252.82   $252.80   $252.80  
  7 purchase totals = $633.29       $694.4743   $694.47   $694.50   $694.40