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 $146.86   11.456%   $163.6843   $163.68   $163.70   $163.70  
  Purchase #2 $8.76   13.630%   $9.954   $9.95   $9.95   $10.00  
  Purchase #3 $165.42   10.258%   $182.3888   $182.39   $182.40   $182.40  
  Purchase #4 $36.41   3.396%   $37.6465   $37.65   $37.65   $37.60  
  Purchase #5 $133.87   5.249%   $140.8968   $140.90   $140.90   $140.90  
  Purchase #6 $161.80   10.395%   $178.6191   $178.62   $178.60   $178.60  
  Purchase #7 $38.95   9.814%   $42.7726   $42.77   $42.75   $42.80  
  7 purchase totals = $692.07       $755.9621   $755.96   $755.95   $756.00