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	$37.53	4.247%	$39.1239	$39.12	$39.10	$39.10
Purchase #2	$198.28	7.740%	$213.6269	$213.63	$213.65	$213.60
Purchase #3	$171.78	11.604%	$191.7134	$191.71	$191.70	$191.70
Purchase #4	$201.85	4.307%	$210.5437	$210.54	$210.55	$210.50
Purchase #5	$84.62	6.123%	$89.8013	$89.80	$89.80	$89.80
Purchase #6	$70.38	4.479%	$73.5323	$73.53	$73.55	$73.50
Purchase #7	$232.73	9.356%	$254.5042	$254.50	$254.50	$254.50
7 purchase totals =	$997.17		$1,072.8457	$1,072.83	$1,072.85	$1,072.70