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	$87.78	4.377%	$91.6221	$91.62	$91.60	$91.60
Purchase #2	$41.43	3.109%	$42.7181	$42.72	$42.70	$42.70
Purchase #3	$151.74	11.400%	$169.0384	$169.04	$169.05	$169.00
Purchase #4	$163.95	3.848%	$170.2588	$170.26	$170.25	$170.30
Purchase #5	$105.25	13.598%	$119.5619	$119.56	$119.55	$119.60
Purchase #6	$41.71	11.144%	$46.3582	$46.36	$46.35	$46.40
Purchase #7	$156.92	5.507%	$165.5616	$165.56	$165.55	$165.60
7 purchase totals =	$748.78		$805.1191	$805.12	$805.05	$805.20