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 $176.49   11.820%   $197.3511   $197.35   $197.35   $197.40  
  Purchase #2 $203.89   5.711%   $215.5342   $215.53   $215.55   $215.50  
  Purchase #3 $246.82   7.641%   $265.6795   $265.68   $265.70   $265.70  
  Purchase #4 $190.95   12.497%   $214.813   $214.81   $214.80   $214.80  
  Purchase #5 $147.41   4.580%   $154.1614   $154.16   $154.15   $154.20  
  Purchase #6 $218.55   4.236%   $227.8078   $227.81   $227.80   $227.80  
  Purchase #7 $87.35   11.285%   $97.2074   $97.21   $97.20   $97.20  
  7 purchase totals = $1,271.46       $1,372.5544   $1,372.55   $1,372.55   $1,372.60