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 $148.72   12.722%   $167.6402   $167.64   $167.65   $167.60  
  Purchase #2 $184.87   9.537%   $202.5011   $202.50   $202.50   $202.50  
  Purchase #3 $75.84   9.855%   $83.314   $83.31   $83.30   $83.30  
  Purchase #4 $85.61   10.839%   $94.8893   $94.89   $94.90   $94.90  
  Purchase #5 $35.63   3.366%   $36.8293   $36.83   $36.85   $36.80  
  Purchase #6 $65.76   12.608%   $74.051   $74.05   $74.05   $74.10  
  Purchase #7 $140.65   4.629%   $147.1607   $147.16   $147.15   $147.20  
  7 purchase totals = $737.08       $806.3856   $806.38   $806.40   $806.40