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 $22.68   10.270%   $25.0092   $25.01   $25.00   $25.00  
  Purchase #2 $85.90   12.772%   $96.8711   $96.87   $96.85   $96.90  
  Purchase #3 $169.62   9.403%   $185.5694   $185.57   $185.55   $185.60  
  Purchase #4 $247.95   12.443%   $278.8024   $278.80   $278.80   $278.80  
  Purchase #5 $52.62   12.707%   $59.3064   $59.31   $59.30   $59.30  
  Purchase #6 $31.81   4.699%   $33.3048   $33.30   $33.30   $33.30  
  Purchase #7 $56.26   13.847%   $64.0503   $64.05   $64.05   $64.10  
  7 purchase totals = $666.84       $742.9136   $742.91   $742.85   $743.00