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	$78.96	12.281%	$88.6571	$88.66	$88.65	$88.70
Purchase #2	$14.59	8.561%	$15.839	$15.84	$15.85	$15.80
Purchase #3	$73.75	3.499%	$76.3305	$76.33	$76.35	$76.30
Purchase #4	$37.55	3.512%	$38.8688	$38.87	$38.85	$38.90
Purchase #5	$112.66	13.467%	$127.8319	$127.83	$127.85	$127.80
Purchase #6	$165.55	3.498%	$171.3409	$171.34	$171.35	$171.30
Purchase #7	$56.63	6.456%	$60.286	$60.29	$60.30	$60.30
7 purchase totals =	$539.69		$579.1542	$579.16	$579.20	$579.10