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 $222.73   7.304%   $238.9982   $239.00   $239.00   $239.00  
  Purchase #2 $96.94   4.845%   $101.6367   $101.64   $101.65   $101.60  
  Purchase #3 $109.59   11.477%   $122.1676   $122.17   $122.15   $122.20  
  Purchase #4 $26.84   10.217%   $29.5822   $29.58   $29.60   $29.60  
  Purchase #5 $186.88   11.578%   $208.517   $208.52   $208.50   $208.50  
  Purchase #6 $235.90   13.647%   $268.0933   $268.09   $268.10   $268.10  
  Purchase #7 $94.48   7.405%   $101.4762   $101.48   $101.50   $101.50  
  7 purchase totals = $973.36       $1,070.4712   $1,070.48   $1,070.50   $1,070.50