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 $60.87   9.844%   $66.862   $66.86   $66.85   $66.90  
  Purchase #2 $236.45   4.363%   $246.7663   $246.77   $246.75   $246.80  
  Purchase #3 $117.76   12.671%   $132.6814   $132.68   $132.70   $132.70  
  Purchase #4 $115.88   6.789%   $123.7471   $123.75   $123.75   $123.70  
  Purchase #5 $179.36   13.361%   $203.3243   $203.32   $203.30   $203.30  
  Purchase #6 $143.42   6.548%   $152.8111   $152.81   $152.80   $152.80  
  Purchase #7 $58.48   11.269%   $65.0701   $65.07   $65.05   $65.10  
  7 purchase totals = $912.22       $991.2623   $991.26   $991.20   $991.30