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 $161.55   13.638%   $183.5822   $183.58   $183.60   $183.60  
  Purchase #2 $179.98   10.420%   $198.7339   $198.73   $198.75   $198.70  
  Purchase #3 $42.30   10.192%   $46.6112   $46.61   $46.60   $46.60  
  Purchase #4 $195.45   12.178%   $219.2519   $219.25   $219.25   $219.30  
  Purchase #5 $34.26   8.216%   $37.0748   $37.07   $37.05   $37.10  
  Purchase #6 $138.73   13.114%   $156.9231   $156.92   $156.90   $156.90  
  Purchase #7 $212.63   3.726%   $220.5526   $220.55   $220.55   $220.60  
  7 purchase totals = $964.90       $1,062.7297   $1,062.71   $1,062.70   $1,062.80