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	$120.50	7.819%	$129.9219	$129.92	$129.90	$129.90
Purchase #2	$12.49	13.432%	$14.1677	$14.17	$14.15	$14.20
Purchase #3	$71.57	11.234%	$79.6102	$79.61	$79.60	$79.60
Purchase #4	$41.72	6.578%	$44.4643	$44.46	$44.45	$44.50
Purchase #5	$51.28	5.155%	$53.9235	$53.92	$53.90	$53.90
Purchase #6	$71.57	9.119%	$78.0965	$78.10	$78.10	$78.10
Purchase #7	$180.41	3.284%	$186.3347	$186.33	$186.35	$186.30
7 purchase totals =	$549.54		$586.5188	$586.51	$586.45	$586.50