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 $61.43   9.233%   $67.1018   $67.10   $67.10   $67.10  
  Purchase #2 $12.92   10.811%   $14.3168   $14.32   $14.30   $14.30  
  Purchase #3 $182.81   13.759%   $207.9628   $207.96   $207.95   $208.00  
  Purchase #4 $50.67   9.290%   $55.3772   $55.38   $55.40   $55.40  
  Purchase #5 $60.53   10.514%   $66.8941   $66.89   $66.90   $66.90  
  Purchase #6 $169.44   10.107%   $186.5653   $186.57   $186.55   $186.60  
  Purchase #7 $86.91   8.801%   $94.5589   $94.56   $94.55   $94.60  
  7 purchase totals = $624.71       $692.7769   $692.78   $692.75   $692.90