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 $211.63   5.383%   $223.022   $223.02   $223.00   $223.00  
  Purchase #2 $136.91   12.197%   $153.6089   $153.61   $153.60   $153.60  
  Purchase #3 $8.30   11.605%   $9.2632   $9.26   $9.25   $9.30  
  Purchase #4 $121.91   3.390%   $126.0427   $126.04   $126.05   $126.00  
  Purchase #5 $62.51   5.127%   $65.7149   $65.71   $65.70   $65.70  
  Purchase #6 $244.76   6.403%   $260.432   $260.43   $260.45   $260.40  
  Purchase #7 $14.83   11.239%   $16.4967   $16.50   $16.50   $16.50  
  7 purchase totals = $800.85       $854.5804   $854.57   $854.55   $854.50