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	$37.96	9.449%	$41.5468	$41.55	$41.55	$41.50
Purchase #2	$36.76	4.128%	$38.2775	$38.28	$38.30	$38.30
Purchase #3	$174.93	3.241%	$180.5995	$180.60	$180.60	$180.60
Purchase #4	$160.91	7.415%	$172.8415	$172.84	$172.85	$172.80
Purchase #5	$151.34	9.449%	$165.6401	$165.64	$165.65	$165.60
Purchase #6	$150.74	13.729%	$171.4351	$171.44	$171.45	$171.40
Purchase #7	$229.94	8.619%	$249.7585	$249.76	$249.75	$249.80
7 purchase totals =	$942.58		$1,020.0990	$1,020.11	$1,020.15	$1,020.00