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 $247.73   5.767%   $262.0166   $262.02   $262.00   $262.00  
  Purchase #2 $190.86   4.297%   $199.0613   $199.06   $199.05   $199.10  
  Purchase #3 $241.94   5.824%   $256.0306   $256.03   $256.05   $256.00  
  Purchase #4 $215.71   8.438%   $233.9116   $233.91   $233.90   $233.90  
  Purchase #5 $113.91   7.569%   $122.5318   $122.53   $122.55   $122.50  
  Purchase #6 $169.76   4.650%   $177.6538   $177.65   $177.65   $177.70  
  Purchase #7 $143.69   9.831%   $157.8162   $157.82   $157.80   $157.80  
  7 purchase totals = $1,323.60       $1,409.0219   $1,409.02   $1,409.00   $1,409.00