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 $142.62   12.527%   $160.486   $160.49   $160.50   $160.50  
  Purchase #2 $214.89   11.652%   $239.929   $239.93   $239.95   $239.90  
  Purchase #3 $199.58   8.730%   $217.0033   $217.00   $217.00   $217.00  
  Purchase #4 $43.56   9.601%   $47.7422   $47.74   $47.75   $47.70  
  Purchase #5 $206.34   9.637%   $226.225   $226.23   $226.25   $226.20  
  Purchase #6 $219.96   8.300%   $238.2167   $238.22   $238.20   $238.20  
  Purchase #7 $34.87   6.855%   $37.2603   $37.26   $37.25   $37.30  
  7 purchase totals = $1,061.82       $1,166.8625   $1,166.87   $1,166.90   $1,166.80