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 $204.72   10.238%   $225.6792   $225.68   $225.70   $225.70  
  Purchase #2 $27.69   10.503%   $30.5983   $30.60   $30.60   $30.60  
  Purchase #3 $167.64   5.514%   $176.8837   $176.88   $176.90   $176.90  
  Purchase #4 $32.96   4.735%   $34.5207   $34.52   $34.50   $34.50  
  Purchase #5 $116.42   10.529%   $128.6779   $128.68   $128.70   $128.70  
  Purchase #6 $66.31   9.626%   $72.693   $72.69   $72.70   $72.70  
  Purchase #7 $66.81   11.597%   $74.558   $74.56   $74.55   $74.60  
  7 purchase totals = $682.55       $743.6108   $743.61   $743.65   $743.70