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 $109.39   9.366%   $119.6355   $119.64   $119.65   $119.60  
  Purchase #2 $16.97   7.606%   $18.2607   $18.26   $18.25   $18.30  
  Purchase #3 $131.75   10.122%   $145.0857   $145.09   $145.10   $145.10  
  Purchase #4 $24.44   4.119%   $25.4467   $25.45   $25.45   $25.40  
  Purchase #5 $204.45   10.832%   $226.596   $226.60   $226.60   $226.60  
  Purchase #6 $239.37   11.849%   $267.733   $267.73   $267.75   $267.70  
  Purchase #7 $235.92   5.756%   $249.4996   $249.50   $249.50   $249.50  
  7 purchase totals = $962.29       $1,052.2572   $1,052.27   $1,052.30   $1,052.20