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	$52.93	8.745%	$57.5587	$57.56	$57.55	$57.60
Purchase #2	$48.80	13.728%	$55.4993	$55.50	$55.50	$55.50
Purchase #3	$109.27	8.526%	$118.5864	$118.59	$118.60	$118.60
Purchase #4	$171.73	5.331%	$180.8849	$180.88	$180.90	$180.90
Purchase #5	$202.59	4.362%	$211.427	$211.43	$211.45	$211.40
Purchase #6	$75.99	8.406%	$82.3777	$82.38	$82.40	$82.40
Purchase #7	$79.30	5.675%	$83.8003	$83.80	$83.80	$83.80
7 purchase totals =	$740.61		$790.1343	$790.14	$790.20	$790.20