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	$55.80	3.364%	$57.6771	$57.68	$57.70	$57.70
Purchase #2	$137.71	11.850%	$154.0286	$154.03	$154.05	$154.00
Purchase #3	$123.63	6.550%	$131.7278	$131.73	$131.75	$131.70
Purchase #4	$189.91	9.275%	$207.5242	$207.52	$207.50	$207.50
Purchase #5	$237.82	11.347%	$264.8054	$264.81	$264.80	$264.80
Purchase #6	$39.66	4.279%	$41.3571	$41.36	$41.35	$41.40
Purchase #7	$179.82	13.828%	$204.6855	$204.69	$204.70	$204.70
7 purchase totals =	$964.35		$1,061.8057	$1,061.82	$1,061.85	$1,061.80