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	$42.80	5.141%	$45.0003	$45.00	$45.00	$45.00
Purchase #2	$203.62	9.585%	$223.137	$223.14	$223.15	$223.10
Purchase #3	$78.61	9.262%	$85.8909	$85.89	$85.90	$85.90
Purchase #4	$35.55	5.864%	$37.6347	$37.63	$37.65	$37.60
Purchase #5	$44.48	12.495%	$50.0378	$50.04	$50.05	$50.00
Purchase #6	$200.38	6.648%	$213.7013	$213.70	$213.70	$213.70
Purchase #7	$162.35	3.403%	$167.8748	$167.87	$167.85	$167.90
7 purchase totals =	$767.79		$823.2768	$823.27	$823.30	$823.20