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	$50.54	6.675%	$53.9135	$53.91	$53.90	$53.90
Purchase #2	$67.60	10.261%	$74.5364	$74.54	$74.55	$74.50
Purchase #3	$102.43	7.189%	$109.7937	$109.79	$109.80	$109.80
Purchase #4	$122.37	12.258%	$137.3701	$137.37	$137.35	$137.40
Purchase #5	$206.51	7.628%	$222.2626	$222.26	$222.25	$222.30
Purchase #6	$89.42	10.661%	$98.9531	$98.95	$98.95	$99.00
Purchase #7	$178.74	6.807%	$190.9068	$190.91	$190.90	$190.90
7 purchase totals =	$817.61		$887.7362	$887.73	$887.70	$887.80