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	$30.93	5.260%	$32.5569	$32.56	$32.55	$32.60
Purchase #2	$42.52	5.139%	$44.7051	$44.71	$44.70	$44.70
Purchase #3	$234.98	4.538%	$245.6434	$245.64	$245.65	$245.60
Purchase #4	$8.94	13.403%	$10.1382	$10.14	$10.15	$10.10
Purchase #5	$174.63	12.510%	$196.4762	$196.48	$196.50	$196.50
Purchase #6	$140.99	12.617%	$158.7787	$158.78	$158.80	$158.80
Purchase #7	$53.56	3.274%	$55.3136	$55.31	$55.30	$55.30
7 purchase totals =	$686.55		$743.6121	$743.62	$743.65	$743.60