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	$126.28	5.504%	$133.2305	$133.23	$133.25	$133.20
Purchase #2	$98.66	6.418%	$104.992	$104.99	$105.00	$105.00
Purchase #3	$54.33	13.588%	$61.7124	$61.71	$61.70	$61.70
Purchase #4	$190.40	11.419%	$212.1418	$212.14	$212.15	$212.10
Purchase #5	$70.95	10.309%	$78.2642	$78.26	$78.25	$78.30
Purchase #6	$179.46	6.329%	$190.818	$190.82	$190.80	$190.80
Purchase #7	$38.79	3.126%	$40.0026	$40.00	$40.00	$40.00
7 purchase totals =	$758.87		$821.1615	$821.15	$821.15	$821.10