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 $195.87   10.580%   $216.593   $216.59   $216.60   $216.60  
  Purchase #2 $240.47   3.861%   $249.7545   $249.75   $249.75   $249.80  
  Purchase #3 $8.75   5.123%   $9.1983   $9.20   $9.20   $9.20  
  Purchase #4 $166.92   12.627%   $187.997   $188.00   $188.00   $188.00  
  Purchase #5 $177.36   4.607%   $185.531   $185.53   $185.55   $185.50  
  Purchase #6 $39.74   3.421%   $41.0995   $41.10   $41.10   $41.10  
  Purchase #7 $236.53   8.152%   $255.8119   $255.81   $255.80   $255.80  
  7 purchase totals = $1,065.64       $1,145.9852   $1,145.98   $1,146.00   $1,146.00