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	$106.31	4.794%	$111.4065	$111.41	$111.40	$111.40
Purchase #2	$71.94	12.632%	$81.0275	$81.03	$81.05	$81.00
Purchase #3	$249.46	12.141%	$279.7469	$279.75	$279.75	$279.70
Purchase #4	$83.91	7.419%	$90.1353	$90.14	$90.15	$90.10
Purchase #5	$240.81	8.205%	$260.5685	$260.57	$260.55	$260.60
Purchase #6	$40.79	12.187%	$45.7611	$45.76	$45.75	$45.80
Purchase #7	$31.71	4.789%	$33.2286	$33.23	$33.25	$33.20
7 purchase totals =	$824.93		$901.8744	$901.89	$901.90	$901.80