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	$36.31	4.565%	$37.9676	$37.97	$37.95	$38.00
Purchase #2	$40.64	10.862%	$45.0543	$45.05	$45.05	$45.10
Purchase #3	$168.98	11.194%	$187.8956	$187.90	$187.90	$187.90
Purchase #4	$50.82	13.612%	$57.7376	$57.74	$57.75	$57.70
Purchase #5	$111.50	13.639%	$126.7075	$126.71	$126.70	$126.70
Purchase #6	$126.41	12.251%	$141.8965	$141.90	$141.90	$141.90
Purchase #7	$170.44	11.787%	$190.5298	$190.53	$190.55	$190.50
7 purchase totals =	$705.10		$787.7889	$787.80	$787.80	$787.80