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	$105.39	6.179%	$111.902	$111.90	$111.90	$111.90
Purchase #2	$70.82	11.866%	$79.2235	$79.22	$79.20	$79.20
Purchase #3	$11.95	12.296%	$13.4194	$13.42	$13.40	$13.40
Purchase #4	$188.28	13.254%	$213.2346	$213.23	$213.25	$213.20
Purchase #5	$67.62	4.631%	$70.7515	$70.75	$70.75	$70.80
Purchase #6	$67.80	5.283%	$71.3819	$71.38	$71.40	$71.40
Purchase #7	$202.35	13.223%	$229.1067	$229.11	$229.10	$229.10
7 purchase totals =	$714.21		$789.0196	$789.01	$789.00	$789.00