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 $196.42   8.771%   $213.648   $213.65   $213.65   $213.60  
  Purchase #2 $33.56   3.387%   $34.6967   $34.70   $34.70   $34.70  
  Purchase #3 $129.38   8.684%   $140.6154   $140.62   $140.60   $140.60  
  Purchase #4 $244.77   3.357%   $252.9869   $252.99   $253.00   $253.00  
  Purchase #5 $111.56   5.415%   $117.601   $117.60   $117.60   $117.60  
  Purchase #6 $110.79   9.425%   $121.232   $121.23   $121.25   $121.20  
  Purchase #7 $115.82   7.462%   $124.4625   $124.46   $124.45   $124.50  
  7 purchase totals = $942.30       $1,005.2425   $1,005.25   $1,005.25   $1,005.20