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 $161.75   11.103%   $179.7091   $179.71   $179.70   $179.70  
  Purchase #2 $77.58   12.575%   $87.3357   $87.34   $87.35   $87.30  
  Purchase #3 $170.97   7.866%   $184.4185   $184.42   $184.40   $184.40  
  Purchase #4 $80.43   7.618%   $86.5572   $86.56   $86.55   $86.60  
  Purchase #5 $229.56   11.781%   $256.6045   $256.60   $256.60   $256.60  
  Purchase #6 $182.91   10.669%   $202.4247   $202.42   $202.40   $202.40  
  Purchase #7 $63.48   11.272%   $70.6355   $70.64   $70.65   $70.60  
  7 purchase totals = $966.68       $1,067.6852   $1,067.69   $1,067.65   $1,067.60