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 $91.25   3.213%   $94.1819   $94.18   $94.20   $94.20  
  Purchase #2 $36.54   5.373%   $38.5033   $38.50   $38.50   $38.50  
  Purchase #3 $148.92   3.203%   $153.6899   $153.69   $153.70   $153.70  
  Purchase #4 $214.91   5.425%   $226.5689   $226.57   $226.55   $226.60  
  Purchase #5 $69.93   12.732%   $78.8335   $78.83   $78.85   $78.80  
  Purchase #6 $199.27   11.454%   $222.0944   $222.09   $222.10   $222.10  
  Purchase #7 $82.62   12.608%   $93.0367   $93.04   $93.05   $93.00  
  7 purchase totals = $843.44       $906.9086   $906.90   $906.95   $906.90