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 $164.85   12.616%   $185.6475   $185.65   $185.65   $185.60  
  Purchase #2 $66.93   3.589%   $69.3321   $69.33   $69.35   $69.30  
  Purchase #3 $152.66   4.189%   $159.0549   $159.05   $159.05   $159.10  
  Purchase #4 $175.64   7.464%   $188.7498   $188.75   $188.75   $188.70  
  Purchase #5 $207.63   5.634%   $219.3279   $219.33   $219.35   $219.30  
  Purchase #6 $145.34   12.856%   $164.0249   $164.02   $164.00   $164.00  
  Purchase #7 $185.29   13.762%   $210.7896   $210.79   $210.80   $210.80  
  7 purchase totals = $1,098.34       $1,196.9267   $1,196.92   $1,196.95   $1,196.80