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 $126.59   13.433%   $143.5948   $143.59   $143.60   $143.60  
  Purchase #2 $230.61   8.411%   $250.0066   $250.01   $250.00   $250.00  
  Purchase #3 $214.74   9.282%   $234.6722   $234.67   $234.65   $234.70  
  Purchase #4 $201.65   8.483%   $218.756   $218.76   $218.75   $218.80  
  Purchase #5 $46.99   13.615%   $53.3877   $53.39   $53.40   $53.40  
  Purchase #6 $40.77   12.784%   $45.982   $45.98   $46.00   $46.00  
  Purchase #7 $237.38   3.304%   $245.223   $245.22   $245.20   $245.20  
  7 purchase totals = $1,098.73       $1,191.6223   $1,191.62   $1,191.60   $1,191.70