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 $33.91   5.202%   $35.674   $35.67   $35.65   $35.70  
  Purchase #2 $130.50   5.715%   $137.9581   $137.96   $137.95   $138.00  
  Purchase #3 $122.31   3.252%   $126.2875   $126.29   $126.30   $126.30  
  Purchase #4 $87.65   12.624%   $98.7149   $98.71   $98.70   $98.70  
  Purchase #5 $184.31   12.715%   $207.745   $207.75   $207.75   $207.70  
  Purchase #6 $139.78   8.382%   $151.4964   $151.50   $151.50   $151.50  
  Purchase #7 $244.99   8.842%   $266.652   $266.65   $266.65   $266.70  
  7 purchase totals = $943.45       $1,024.5279   $1,024.53   $1,024.50   $1,024.60