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 $162.72   13.228%   $184.2446   $184.24   $184.25   $184.20  
  Purchase #2 $24.70   8.744%   $26.8598   $26.86   $26.85   $26.90  
  Purchase #3 $75.99   3.161%   $78.392   $78.39   $78.40   $78.40  
  Purchase #4 $241.32   13.121%   $272.9836   $272.98   $273.00   $273.00  
  Purchase #5 $216.54   4.834%   $227.0075   $227.01   $227.00   $227.00  
  Purchase #6 $44.80   8.796%   $48.7406   $48.74   $48.75   $48.70  
  Purchase #7 $185.32   13.419%   $210.1881   $210.19   $210.20   $210.20  
  7 purchase totals = $951.39       $1,048.4162   $1,048.41   $1,048.45   $1,048.40