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 $63.37   6.712%   $67.6234   $67.62   $67.60   $67.60  
  Purchase #2 $158.52   6.354%   $168.5924   $168.59   $168.60   $168.60  
  Purchase #3 $95.60   8.121%   $103.3637   $103.36   $103.35   $103.40  
  Purchase #4 $212.80   12.365%   $239.1127   $239.11   $239.10   $239.10  
  Purchase #5 $23.76   3.373%   $24.5614   $24.56   $24.55   $24.60  
  Purchase #6 $225.63   3.593%   $233.7369   $233.74   $233.75   $233.70  
  Purchase #7 $49.35   3.295%   $50.9761   $50.98   $51.00   $51.00  
  7 purchase totals = $829.03       $887.9666   $887.96   $887.95   $888.00