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	$78.40	4.742%	$82.1177	$82.12	$82.10	$82.10
Purchase #2	$162.46	11.306%	$180.8277	$180.83	$180.85	$180.80
Purchase #3	$177.66	4.135%	$185.0062	$185.01	$185.00	$185.00
Purchase #4	$158.87	13.371%	$180.1125	$180.11	$180.10	$180.10
Purchase #5	$20.48	7.224%	$21.9595	$21.96	$21.95	$22.00
Purchase #6	$220.76	3.327%	$228.1047	$228.10	$228.10	$228.10
Purchase #7	$87.77	3.718%	$91.0333	$91.03	$91.05	$91.00
7 purchase totals =	$906.40		$969.1616	$969.16	$969.15	$969.10