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 $101.66   11.848%   $113.7047   $113.70   $113.70   $113.70  
  Purchase #2 $140.59   5.196%   $147.8951   $147.90   $147.90   $147.90  
  Purchase #3 $104.99   6.527%   $111.8427   $111.84   $111.85   $111.80  
  Purchase #4 $58.49   4.644%   $61.2063   $61.21   $61.20   $61.20  
  Purchase #5 $250.44   8.312%   $271.2566   $271.26   $271.25   $271.30  
  Purchase #6 $7.81   13.334%   $8.8514   $8.85   $8.85   $8.90  
  Purchase #7 $65.67   3.280%   $67.824   $67.82   $67.80   $67.80  
  7 purchase totals = $729.65       $782.5808   $782.58   $782.55   $782.60