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 $204.82   10.712%   $226.7603   $226.76   $226.75   $226.80  
  Purchase #2 $163.55   4.750%   $171.3186   $171.32   $171.30   $171.30  
  Purchase #3 $67.45   13.526%   $76.5733   $76.57   $76.55   $76.60  
  Purchase #4 $216.79   13.567%   $246.2019   $246.20   $246.20   $246.20  
  Purchase #5 $26.81   12.337%   $30.1175   $30.12   $30.10   $30.10  
  Purchase #6 $221.78   10.346%   $244.7254   $244.73   $244.75   $244.70  
  Purchase #7 $243.54   3.642%   $252.4097   $252.41   $252.40   $252.40  
  7 purchase totals = $1,144.74       $1,248.1067   $1,248.11   $1,248.05   $1,248.10