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 $235.50   3.494%   $243.7284   $243.73   $243.75   $243.70  
  Purchase #2 $243.55   9.211%   $265.9834   $265.98   $266.00   $266.00  
  Purchase #3 $138.76   4.348%   $144.7933   $144.79   $144.80   $144.80  
  Purchase #4 $59.91   5.602%   $63.2662   $63.27   $63.25   $63.30  
  Purchase #5 $147.35   4.612%   $154.1458   $154.15   $154.15   $154.10  
  Purchase #6 $117.62   9.186%   $128.4246   $128.42   $128.40   $128.40  
  Purchase #7 $21.55   4.780%   $22.5801   $22.58   $22.60   $22.60  
  7 purchase totals = $964.24       $1,022.9218   $1,022.92   $1,022.95   $1,022.90