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	$7.54	4.764%	$7.8992	$7.90	$7.90	$7.90
Purchase #2	$250.50	5.353%	$263.9093	$263.91	$263.90	$263.90
Purchase #3	$200.98	11.400%	$223.8917	$223.89	$223.90	$223.90
Purchase #4	$186.36	6.312%	$198.123	$198.12	$198.10	$198.10
Purchase #5	$26.55	13.510%	$30.1369	$30.14	$30.15	$30.10
Purchase #6	$59.79	4.186%	$62.2928	$62.29	$62.30	$62.30
Purchase #7	$58.38	4.325%	$60.9049	$60.90	$60.90	$60.90
7 purchase totals =	$790.10		$847.1578	$847.15	$847.15	$847.10