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	$35.64	5.173%	$37.4837	$37.48	$37.50	$37.50
Purchase #2	$48.75	7.540%	$52.4258	$52.43	$52.45	$52.40
Purchase #3	$138.80	5.648%	$146.6394	$146.64	$146.65	$146.60
Purchase #4	$138.87	8.231%	$150.3004	$150.30	$150.30	$150.30
Purchase #5	$148.29	11.420%	$165.2247	$165.22	$165.20	$165.20
Purchase #6	$180.85	9.826%	$198.6203	$198.62	$198.60	$198.60
Purchase #7	$250.46	7.836%	$270.086	$270.09	$270.10	$270.10
7 purchase totals =	$941.66		$1,020.7803	$1,020.78	$1,020.80	$1,020.70