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	$84.74	6.102%	$89.9108	$89.91	$89.90	$89.90
Purchase #2	$47.51	13.768%	$54.0512	$54.05	$54.05	$54.10
Purchase #3	$92.97	11.171%	$103.3557	$103.36	$103.35	$103.40
Purchase #4	$127.77	4.183%	$133.1146	$133.11	$133.10	$133.10
Purchase #5	$224.48	4.479%	$234.5345	$234.53	$234.55	$234.50
Purchase #6	$244.88	12.662%	$275.8867	$275.89	$275.90	$275.90
Purchase #7	$44.31	5.446%	$46.7231	$46.72	$46.70	$46.70
7 purchase totals =	$866.66		$937.5766	$937.57	$937.55	$937.60