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	$34.70	3.223%	$35.8184	$35.82	$35.80	$35.80
Purchase #2	$177.90	4.465%	$185.8432	$185.84	$185.85	$185.80
Purchase #3	$37.69	7.459%	$40.5013	$40.50	$40.50	$40.50
Purchase #4	$168.51	13.623%	$191.4661	$191.47	$191.45	$191.50
Purchase #5	$138.61	6.242%	$147.262	$147.26	$147.25	$147.30
Purchase #6	$57.50	6.820%	$61.4215	$61.42	$61.40	$61.40
Purchase #7	$222.28	12.408%	$249.8605	$249.86	$249.85	$249.90
7 purchase totals =	$837.19		$912.1730	$912.17	$912.10	$912.20