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 $232.99   5.587%   $246.0072   $246.01   $246.00   $246.00  
  Purchase #2 $214.97   12.396%   $241.6177   $241.62   $241.60   $241.60  
  Purchase #3 $13.95   11.644%   $15.5743   $15.57   $15.55   $15.60  
  Purchase #4 $168.35   13.314%   $190.7641   $190.76   $190.75   $190.80  
  Purchase #5 $221.96   11.823%   $248.2023   $248.20   $248.20   $248.20  
  Purchase #6 $79.89   10.305%   $88.1227   $88.12   $88.10   $88.10  
  Purchase #7 $237.58   5.290%   $250.148   $250.15   $250.15   $250.10  
  7 purchase totals = $1,169.69       $1,280.4363   $1,280.43   $1,280.35   $1,280.40