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 $250.76   4.873%   $262.9795   $262.98   $263.00   $263.00  
  Purchase #2 $103.33   11.113%   $114.8131   $114.81   $114.80   $114.80  
  Purchase #3 $152.92   11.806%   $170.9737   $170.97   $170.95   $171.00  
  Purchase #4 $177.64   3.386%   $183.6549   $183.65   $183.65   $183.70  
  Purchase #5 $213.54   5.656%   $225.6178   $225.62   $225.60   $225.60  
  Purchase #6 $41.73   4.461%   $43.5916   $43.59   $43.60   $43.60  
  Purchase #7 $29.42   13.601%   $33.4214   $33.42   $33.40   $33.40  
  7 purchase totals = $969.34       $1,035.0520   $1,035.04   $1,035.00   $1,035.10