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	$28.72	7.797%	$30.9593	$30.96	$30.95	$31.00
Purchase #2	$115.65	7.738%	$124.599	$124.60	$124.60	$124.60
Purchase #3	$155.98	6.385%	$165.9393	$165.94	$165.95	$165.90
Purchase #4	$206.72	8.148%	$223.5635	$223.56	$223.55	$223.60
Purchase #5	$25.31	11.326%	$28.1766	$28.18	$28.20	$28.20
Purchase #6	$143.69	11.832%	$160.6914	$160.69	$160.70	$160.70
Purchase #7	$99.25	6.669%	$105.869	$105.87	$105.85	$105.90
7 purchase totals =	$775.32		$839.7981	$839.80	$839.80	$839.90