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 $141.56   7.803%   $152.6059   $152.61   $152.60   $152.60  
  Purchase #2 $76.58   4.208%   $79.8025   $79.80   $79.80   $79.80  
  Purchase #3 $215.28   6.774%   $229.8631   $229.86   $229.85   $229.90  
  Purchase #4 $156.27   6.695%   $166.7323   $166.73   $166.75   $166.70  
  Purchase #5 $190.83   8.752%   $207.5314   $207.53   $207.55   $207.50  
  Purchase #6 $149.59   4.640%   $156.531   $156.53   $156.55   $156.50  
  Purchase #7 $228.37   5.491%   $240.9098   $240.91   $240.90   $240.90  
  7 purchase totals = $1,158.48       $1,233.9760   $1,233.97   $1,234.00   $1,233.90