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 $94.81   8.622%   $102.9845   $102.98   $103.00   $103.00  
  Purchase #2 $200.95   8.157%   $217.3415   $217.34   $217.35   $217.30  
  Purchase #3 $81.40   5.206%   $85.6377   $85.64   $85.65   $85.60  
  Purchase #4 $31.97   13.689%   $36.3464   $36.35   $36.35   $36.30  
  Purchase #5 $160.55   3.782%   $166.622   $166.62   $166.60   $166.60  
  Purchase #6 $226.90   12.215%   $254.6158   $254.62   $254.60   $254.60  
  Purchase #7 $187.92   9.767%   $206.2741   $206.27   $206.25   $206.30  
  7 purchase totals = $984.50       $1,069.8220   $1,069.82   $1,069.80   $1,069.70