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 $246.97   10.759%   $273.5415   $273.54   $273.55   $273.50  
  Purchase #2 $205.92   9.239%   $224.9449   $224.94   $224.95   $224.90  
  Purchase #3 $52.73   9.273%   $57.6197   $57.62   $57.60   $57.60  
  Purchase #4 $117.65   3.285%   $121.5148   $121.51   $121.50   $121.50  
  Purchase #5 $83.44   4.114%   $86.8727   $86.87   $86.85   $86.90  
  Purchase #6 $157.91   3.791%   $163.8964   $163.90   $163.90   $163.90  
  Purchase #7 $246.76   7.453%   $265.151   $265.15   $265.15   $265.20  
  7 purchase totals = $1,111.38       $1,193.5410   $1,193.53   $1,193.50   $1,193.50