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 $203.41   3.107%   $209.7299   $209.73   $209.75   $209.70  
  Purchase #2 $179.42   8.248%   $194.2186   $194.22   $194.20   $194.20  
  Purchase #3 $22.77   6.186%   $24.1786   $24.18   $24.20   $24.20  
  Purchase #4 $5.74   12.115%   $6.4354   $6.44   $6.45   $6.40  
  Purchase #5 $31.76   7.562%   $34.1617   $34.16   $34.15   $34.20  
  Purchase #6 $233.30   5.302%   $245.6696   $245.67   $245.65   $245.70  
  Purchase #7 $176.67   3.358%   $182.6026   $182.60   $182.60   $182.60  
  7 purchase totals = $853.07       $896.9964   $897.00   $897.00   $897.00