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 $109.99   7.763%   $118.5285   $118.53   $118.55   $118.50  
  Purchase #2 $250.53   13.219%   $283.6476   $283.65   $283.65   $283.60  
  Purchase #3 $213.37   11.153%   $237.1672   $237.17   $237.15   $237.20  
  Purchase #4 $92.83   5.333%   $97.7806   $97.78   $97.80   $97.80  
  Purchase #5 $208.53   11.768%   $233.0698   $233.07   $233.05   $233.10  
  Purchase #6 $123.78   12.189%   $138.8675   $138.87   $138.85   $138.90  
  Purchase #7 $54.40   7.700%   $58.5888   $58.59   $58.60   $58.60  
  7 purchase totals = $1,053.43       $1,167.6500   $1,167.66   $1,167.65   $1,167.70