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 $211.73   10.513%   $233.9892   $233.99   $234.00   $234.00  
  Purchase #2 $169.30   13.834%   $192.721   $192.72   $192.70   $192.70  
  Purchase #3 $201.27   10.156%   $221.711   $221.71   $221.70   $221.70  
  Purchase #4 $97.65   8.815%   $106.2578   $106.26   $106.25   $106.30  
  Purchase #5 $248.90   13.404%   $282.2626   $282.26   $282.25   $282.30  
  Purchase #6 $150.84   4.256%   $157.2598   $157.26   $157.25   $157.30  
  Purchase #7 $184.33   5.564%   $194.5861   $194.59   $194.60   $194.60  
  7 purchase totals = $1,264.02       $1,388.7875   $1,388.79   $1,388.75   $1,388.90