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	$70.52	13.650%	$80.146	$80.15	$80.15	$80.10
Purchase #2	$73.61	6.822%	$78.6317	$78.63	$78.65	$78.60
Purchase #3	$152.34	6.453%	$162.1705	$162.17	$162.15	$162.20
Purchase #4	$31.65	8.467%	$34.3298	$34.33	$34.35	$34.30
Purchase #5	$243.93	3.734%	$253.0383	$253.04	$253.05	$253.00
Purchase #6	$38.25	3.700%	$39.6653	$39.67	$39.65	$39.70
Purchase #7	$215.95	6.700%	$230.4187	$230.42	$230.40	$230.40
7 purchase totals =	$826.25		$878.4003	$878.41	$878.40	$878.30