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 $194.75   3.420%   $201.4105   $201.41   $201.40   $201.40  
  Purchase #2 $68.52   5.345%   $72.1824   $72.18   $72.20   $72.20  
  Purchase #3 $97.33   12.615%   $109.6082   $109.61   $109.60   $109.60  
  Purchase #4 $204.61   10.288%   $225.6603   $225.66   $225.65   $225.70  
  Purchase #5 $162.51   8.358%   $176.0926   $176.09   $176.10   $176.10  
  Purchase #6 $22.83   3.242%   $23.5701   $23.57   $23.55   $23.60  
  Purchase #7 $70.41   5.523%   $74.2987   $74.30   $74.30   $74.30  
  7 purchase totals = $820.96       $882.8228   $882.82   $882.80   $882.90