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 $61.25   8.764%   $66.618   $66.62   $66.60   $66.60  
  Purchase #2 $70.72   5.291%   $74.4618   $74.46   $74.45   $74.50  
  Purchase #3 $128.84   8.191%   $139.3933   $139.39   $139.40   $139.40  
  Purchase #4 $236.30   12.854%   $266.674   $266.67   $266.65   $266.70  
  Purchase #5 $205.67   8.867%   $223.9068   $223.91   $223.90   $223.90  
  Purchase #6 $66.27   5.644%   $70.0103   $70.01   $70.00   $70.00  
  Purchase #7 $13.66   6.860%   $14.5971   $14.60   $14.60   $14.60  
  7 purchase totals = $782.71       $855.6613   $855.66   $855.60   $855.70