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 $249.86   5.249%   $262.9752   $262.98   $263.00   $263.00  
  Purchase #2 $11.56   3.288%   $11.9401   $11.94   $11.95   $11.90  
  Purchase #3 $152.92   8.362%   $165.7072   $165.71   $165.70   $165.70  
  Purchase #4 $241.86   10.209%   $266.5515   $266.55   $266.55   $266.60  
  Purchase #5 $23.58   13.572%   $26.7803   $26.78   $26.80   $26.80  
  Purchase #6 $208.43   6.528%   $222.0363   $222.04   $222.05   $222.00  
  Purchase #7 $177.49   11.539%   $197.9706   $197.97   $197.95   $198.00  
  7 purchase totals = $1,065.70       $1,153.9612   $1,153.97   $1,154.00   $1,154.00