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 $58.99   12.745%   $66.5083   $66.51   $66.50   $66.50  
  Purchase #2 $25.38   8.682%   $27.5835   $27.58   $27.60   $27.60  
  Purchase #3 $119.44   11.625%   $133.3249   $133.32   $133.30   $133.30  
  Purchase #4 $161.70   11.113%   $179.6697   $179.67   $179.65   $179.70  
  Purchase #5 $225.76   3.483%   $233.6232   $233.62   $233.60   $233.60  
  Purchase #6 $192.31   10.777%   $213.0352   $213.04   $213.05   $213.00  
  Purchase #7 $160.36   7.698%   $172.7045   $172.70   $172.70   $172.70  
  7 purchase totals = $943.94       $1,026.4493   $1,026.44   $1,026.40   $1,026.40