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 $172.85   9.735%   $189.6769   $189.68   $189.70   $189.70  
  Purchase #2 $58.85   4.770%   $61.6571   $61.66   $61.65   $61.70  
  Purchase #3 $63.27   3.543%   $65.5117   $65.51   $65.50   $65.50  
  Purchase #4 $208.73   9.259%   $228.0563   $228.06   $228.05   $228.10  
  Purchase #5 $197.89   10.752%   $219.1671   $219.17   $219.15   $219.20  
  Purchase #6 $68.50   11.810%   $76.5899   $76.59   $76.60   $76.60  
  Purchase #7 $169.89   7.853%   $183.2315   $183.23   $183.25   $183.20  
  7 purchase totals = $939.98       $1,023.8905   $1,023.90   $1,023.90   $1,024.00