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 $222.54   4.577%   $232.7257   $232.73   $232.75   $232.70  
  Purchase #2 $192.33   5.614%   $203.1274   $203.13   $203.15   $203.10  
  Purchase #3 $75.48   12.593%   $84.9852   $84.99   $85.00   $85.00  
  Purchase #4 $147.66   13.127%   $167.0433   $167.04   $167.05   $167.00  
  Purchase #5 $227.72   8.734%   $247.6091   $247.61   $247.60   $247.60  
  Purchase #6 $200.63   5.403%   $211.47   $211.47   $211.45   $211.50  
  Purchase #7 $97.54   11.235%   $108.4986   $108.50   $108.50   $108.50  
  7 purchase totals = $1,163.90       $1,255.4593   $1,255.47   $1,255.50   $1,255.40