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 $158.33   10.317%   $174.6649   $174.66   $174.65   $174.70  
  Purchase #2 $229.62   4.654%   $240.3065   $240.31   $240.30   $240.30  
  Purchase #3 $163.43   9.620%   $179.152   $179.15   $179.15   $179.20  
  Purchase #4 $178.91   8.244%   $193.6593   $193.66   $193.65   $193.70  
  Purchase #5 $23.33   11.611%   $26.0388   $26.04   $26.05   $26.00  
  Purchase #6 $115.60   10.758%   $128.0362   $128.04   $128.05   $128.00  
  Purchase #7 $100.43   5.171%   $105.6232   $105.62   $105.60   $105.60  
  7 purchase totals = $969.65       $1,047.4809   $1,047.48   $1,047.45   $1,047.50