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	$50.43	6.839%	$53.8789	$53.88	$53.90	$53.90
Purchase #2	$79.77	3.582%	$82.6274	$82.63	$82.65	$82.60
Purchase #3	$64.44	11.106%	$71.5967	$71.60	$71.60	$71.60
Purchase #4	$8.50	10.425%	$9.3861	$9.39	$9.40	$9.40
Purchase #5	$105.74	4.808%	$110.824	$110.82	$110.80	$110.80
Purchase #6	$145.58	11.678%	$162.5808	$162.58	$162.60	$162.60
Purchase #7	$40.59	10.281%	$44.7631	$44.76	$44.75	$44.80
7 purchase totals =	$495.05		$535.6570	$535.66	$535.70	$535.70