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 $105.60   13.281%   $119.6247   $119.62   $119.60   $119.60  
  Purchase #2 $199.34   5.177%   $209.6598   $209.66   $209.65   $209.70  
  Purchase #3 $9.37   13.455%   $10.6307   $10.63   $10.65   $10.60  
  Purchase #4 $235.93   3.729%   $244.7278   $244.73   $244.75   $244.70  
  Purchase #5 $78.33   3.205%   $80.8405   $80.84   $80.85   $80.80  
  Purchase #6 $33.31   5.506%   $35.144   $35.14   $35.15   $35.10  
  Purchase #7 $38.96   10.532%   $43.0633   $43.06   $43.05   $43.10  
  7 purchase totals = $700.84       $743.6908   $743.68   $743.70   $743.60