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	$36.32	4.356%	$37.9021	$37.90	$37.90	$37.90
Purchase #2	$183.69	4.315%	$191.6162	$191.62	$191.60	$191.60
Purchase #3	$58.70	9.565%	$64.3147	$64.31	$64.30	$64.30
Purchase #4	$56.64	13.780%	$64.445	$64.45	$64.45	$64.40
Purchase #5	$106.38	4.603%	$111.2767	$111.28	$111.30	$111.30
Purchase #6	$41.53	11.582%	$46.34	$46.34	$46.35	$46.30
Purchase #7	$58.83	6.132%	$62.4375	$62.44	$62.45	$62.40
7 purchase totals =	$542.09		$578.3322	$578.34	$578.35	$578.20