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 $67.62   11.709%   $75.5376   $75.54   $75.55   $75.50  
  Purchase #2 $207.85   9.706%   $228.0239   $228.02   $228.00   $228.00  
  Purchase #3 $67.97   4.251%   $70.8594   $70.86   $70.85   $70.90  
  Purchase #4 $23.92   11.202%   $26.5995   $26.60   $26.60   $26.60  
  Purchase #5 $213.60   11.189%   $237.4997   $237.50   $237.50   $237.50  
  Purchase #6 $227.52   13.607%   $258.4786   $258.48   $258.50   $258.50  
  Purchase #7 $239.59   6.448%   $255.0388   $255.04   $255.05   $255.00  
  7 purchase totals = $1,048.07       $1,152.0375   $1,152.04   $1,152.05   $1,152.00