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 $138.25   5.504%   $145.8593   $145.86   $145.85   $145.90  
  Purchase #2 $195.31   7.843%   $210.6282   $210.63   $210.65   $210.60  
  Purchase #3 $214.96   10.366%   $237.2428   $237.24   $237.25   $237.20  
  Purchase #4 $176.58   8.852%   $192.2109   $192.21   $192.20   $192.20  
  Purchase #5 $71.53   12.105%   $80.1887   $80.19   $80.20   $80.20  
  Purchase #6 $177.79   7.613%   $191.3252   $191.33   $191.35   $191.30  
  Purchase #7 $226.67   11.288%   $252.2565   $252.26   $252.25   $252.30  
  7 purchase totals = $1,201.09       $1,309.7116   $1,309.72   $1,309.75   $1,309.70