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 $244.75   9.466%   $267.918   $267.92   $267.90   $267.90  
  Purchase #2 $79.48   6.255%   $84.4515   $84.45   $84.45   $84.50  
  Purchase #3 $110.92   8.713%   $120.5845   $120.58   $120.60   $120.60  
  Purchase #4 $174.76   12.312%   $196.2765   $196.28   $196.30   $196.30  
  Purchase #5 $170.70   7.537%   $183.5657   $183.57   $183.55   $183.60  
  Purchase #6 $124.42   9.844%   $136.6679   $136.67   $136.65   $136.70  
  Purchase #7 $98.52   10.658%   $109.0203   $109.02   $109.00   $109.00  
  7 purchase totals = $1,003.55       $1,098.4844   $1,098.49   $1,098.45   $1,098.60