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 $22.88   13.287%   $25.9201   $25.92   $25.90   $25.90  
  Purchase #2 $194.77   9.670%   $213.6043   $213.60   $213.60   $213.60  
  Purchase #3 $37.62   10.845%   $41.6999   $41.70   $41.70   $41.70  
  Purchase #4 $246.60   4.475%   $257.6354   $257.64   $257.65   $257.60  
  Purchase #5 $193.96   10.616%   $214.5508   $214.55   $214.55   $214.60  
  Purchase #6 $116.70   13.658%   $132.6389   $132.64   $132.65   $132.60  
  Purchase #7 $150.46   13.361%   $170.563   $170.56   $170.55   $170.60  
  7 purchase totals = $962.99       $1,056.6124   $1,056.61   $1,056.60   $1,056.60