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 $196.60   5.661%   $207.7295   $207.73   $207.75   $207.70  
  Purchase #2 $211.74   13.469%   $240.2593   $240.26   $240.25   $240.30  
  Purchase #3 $138.32   11.359%   $154.0318   $154.03   $154.05   $154.00  
  Purchase #4 $151.98   9.155%   $165.8938   $165.89   $165.90   $165.90  
  Purchase #5 $33.39   8.745%   $36.31   $36.31   $36.30   $36.30  
  Purchase #6 $145.41   9.665%   $159.4639   $159.46   $159.45   $159.50  
  Purchase #7 $246.31   13.527%   $279.6284   $279.63   $279.65   $279.60  
  7 purchase totals = $1,123.75       $1,243.3167   $1,243.31   $1,243.35   $1,243.30