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 $96.80   9.159%   $105.6659   $105.67   $105.65   $105.70  
  Purchase #2 $241.97   10.394%   $267.1204   $267.12   $267.10   $267.10  
  Purchase #3 $126.27   3.203%   $130.3144   $130.31   $130.30   $130.30  
  Purchase #4 $90.81   4.558%   $94.9491   $94.95   $94.95   $94.90  
  Purchase #5 $238.89   8.649%   $259.5516   $259.55   $259.55   $259.60  
  Purchase #6 $43.88   7.771%   $47.2899   $47.29   $47.30   $47.30  
  Purchase #7 $129.84   7.178%   $139.1599   $139.16   $139.15   $139.20  
  7 purchase totals = $968.46       $1,044.0512   $1,044.05   $1,044.00   $1,044.10