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 $233.76   5.862%   $247.463   $247.46   $247.45   $247.50  
  Purchase #2 $146.80   4.546%   $153.4735   $153.47   $153.45   $153.50  
  Purchase #3 $119.67   8.862%   $130.2752   $130.28   $130.30   $130.30  
  Purchase #4 $28.70   3.838%   $29.8015   $29.80   $29.80   $29.80  
  Purchase #5 $236.84   10.441%   $261.5685   $261.57   $261.55   $261.60  
  Purchase #6 $28.67   3.244%   $29.6001   $29.60   $29.60   $29.60  
  Purchase #7 $147.54   4.655%   $154.408   $154.41   $154.40   $154.40  
  7 purchase totals = $941.98       $1,006.5898   $1,006.59   $1,006.55   $1,006.70