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	$35.89	9.589%	$39.3315	$39.33	$39.35	$39.30
Purchase #2	$195.67	10.537%	$216.2877	$216.29	$216.30	$216.30
Purchase #3	$114.92	11.280%	$127.883	$127.88	$127.90	$127.90
Purchase #4	$56.29	10.319%	$62.0986	$62.10	$62.10	$62.10
Purchase #5	$238.64	6.356%	$253.808	$253.81	$253.80	$253.80
Purchase #6	$54.40	12.738%	$61.3295	$61.33	$61.35	$61.30
Purchase #7	$55.46	11.282%	$61.717	$61.72	$61.70	$61.70
7 purchase totals =	$751.27		$822.4553	$822.46	$822.50	$822.40