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 $242.64   11.199%   $269.8133   $269.81   $269.80   $269.80  
  Purchase #2 $196.60   13.867%   $223.8625   $223.86   $223.85   $223.90  
  Purchase #3 $13.99   4.180%   $14.5748   $14.57   $14.55   $14.60  
  Purchase #4 $91.73   12.488%   $103.1852   $103.19   $103.20   $103.20  
  Purchase #5 $219.46   9.134%   $239.5055   $239.51   $239.50   $239.50  
  Purchase #6 $176.74   7.831%   $190.5805   $190.58   $190.60   $190.60  
  Purchase #7 $106.80   10.836%   $118.3728   $118.37   $118.35   $118.40  
  7 purchase totals = $1,047.96       $1,159.8946   $1,159.89   $1,159.85   $1,160.00