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	$12.61	10.205%	$13.8969	$13.90	$13.90	$13.90
Purchase #2	$13.39	10.597%	$14.8089	$14.81	$14.80	$14.80
Purchase #3	$152.89	10.835%	$169.4556	$169.46	$169.45	$169.50
Purchase #4	$196.32	13.679%	$223.1746	$223.17	$223.15	$223.20
Purchase #5	$169.63	8.685%	$184.3624	$184.36	$184.35	$184.40
Purchase #6	$231.38	6.710%	$246.9056	$246.91	$246.90	$246.90
Purchase #7	$225.88	6.367%	$240.2618	$240.26	$240.25	$240.30
7 purchase totals =	$1,002.10		$1,092.8658	$1,092.87	$1,092.80	$1,093.00