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 $205.41   8.854%   $223.597   $223.60   $223.60   $223.60  
  Purchase #2 $115.35   9.119%   $125.8688   $125.87   $125.85   $125.90  
  Purchase #3 $38.44   8.795%   $41.8208   $41.82   $41.80   $41.80  
  Purchase #4 $222.70   7.466%   $239.3268   $239.33   $239.35   $239.30  
  Purchase #5 $122.45   9.594%   $134.1979   $134.20   $134.20   $134.20  
  Purchase #6 $198.83   5.769%   $210.3005   $210.30   $210.30   $210.30  
  Purchase #7 $241.29   11.177%   $268.259   $268.26   $268.25   $268.30  
  7 purchase totals = $1,144.47       $1,243.3708   $1,243.38   $1,243.35   $1,243.40