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 $231.26   11.861%   $258.6897   $258.69   $258.70   $258.70  
  Purchase #2 $17.61   9.461%   $19.2761   $19.28   $19.30   $19.30  
  Purchase #3 $79.53   7.252%   $85.2975   $85.30   $85.30   $85.30  
  Purchase #4 $205.87   5.495%   $217.1826   $217.18   $217.20   $217.20  
  Purchase #5 $161.25   5.257%   $169.7269   $169.73   $169.75   $169.70  
  Purchase #6 $167.76   9.654%   $183.9556   $183.96   $183.95   $184.00  
  Purchase #7 $248.46   6.394%   $264.3465   $264.35   $264.35   $264.30  
  7 purchase totals = $1,111.74       $1,198.4749   $1,198.49   $1,198.55   $1,198.50