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 $114.46   6.822%   $122.2685   $122.27   $122.25   $122.30  
  Purchase #2 $21.94   13.267%   $24.8508   $24.85   $24.85   $24.90  
  Purchase #3 $198.57   5.378%   $209.2491   $209.25   $209.25   $209.20  
  Purchase #4 $35.33   5.615%   $37.3138   $37.31   $37.30   $37.30  
  Purchase #5 $65.27   6.509%   $69.5184   $69.52   $69.50   $69.50  
  Purchase #6 $247.25   7.296%   $265.2894   $265.29   $265.30   $265.30  
  Purchase #7 $38.34   7.677%   $41.2834   $41.28   $41.30   $41.30  
  7 purchase totals = $721.16       $769.7734   $769.77   $769.75   $769.80