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 $227.49   6.529%   $242.3428   $242.34   $242.35   $242.30  
  Purchase #2 $114.26   7.487%   $122.8146   $122.81   $122.80   $122.80  
  Purchase #3 $107.42   5.226%   $113.0338   $113.03   $113.05   $113.00  
  Purchase #4 $232.61   3.525%   $240.8095   $240.81   $240.80   $240.80  
  Purchase #5 $144.72   5.425%   $152.5711   $152.57   $152.55   $152.60  
  Purchase #6 $97.34   8.657%   $105.7667   $105.77   $105.75   $105.80  
  Purchase #7 $43.98   4.323%   $45.8813   $45.88   $45.90   $45.90  
  7 purchase totals = $967.82       $1,023.2198   $1,023.21   $1,023.20   $1,023.20