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 $233.68   8.171%   $252.774   $252.77   $252.75   $252.80  
  Purchase #2 $63.49   3.453%   $65.6823   $65.68   $65.70   $65.70  
  Purchase #3 $110.34   3.671%   $114.3906   $114.39   $114.40   $114.40  
  Purchase #4 $165.97   4.621%   $173.6395   $173.64   $173.65   $173.60  
  Purchase #5 $10.78   10.372%   $11.8981   $11.90   $11.90   $11.90  
  Purchase #6 $57.31   12.704%   $64.5907   $64.59   $64.60   $64.60  
  Purchase #7 $151.26   12.265%   $169.812   $169.81   $169.80   $169.80  
  7 purchase totals = $792.83       $852.7872   $852.78   $852.80   $852.80