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 $114.74   6.857%   $122.6077   $122.61   $122.60   $122.60  
  Purchase #2 $226.34   7.756%   $243.8949   $243.89   $243.90   $243.90  
  Purchase #3 $8.85   11.416%   $9.8603   $9.86   $9.85   $9.90  
  Purchase #4 $24.67   5.269%   $25.9699   $25.97   $25.95   $26.00  
  Purchase #5 $138.82   4.852%   $145.5555   $145.56   $145.55   $145.60  
  Purchase #6 $216.43   7.155%   $231.9156   $231.92   $231.90   $231.90  
  Purchase #7 $182.63   12.769%   $205.95   $205.95   $205.95   $206.00  
  7 purchase totals = $912.48       $985.7539   $985.76   $985.70   $985.90