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	$173.37	3.844%	$180.0343	$180.03	$180.05	$180.00
Purchase #2	$110.52	9.196%	$120.6834	$120.68	$120.70	$120.70
Purchase #3	$72.95	6.265%	$77.5203	$77.52	$77.50	$77.50
Purchase #4	$181.39	5.282%	$190.971	$190.97	$190.95	$191.00
Purchase #5	$135.83	12.507%	$152.8183	$152.82	$152.80	$152.80
Purchase #6	$109.46	13.557%	$124.2995	$124.30	$124.30	$124.30
Purchase #7	$85.43	4.607%	$89.3658	$89.37	$89.35	$89.40
7 purchase totals =	$868.95		$935.6926	$935.69	$935.65	$935.70