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	$82.31	5.432%	$86.7811	$86.78	$86.80	$86.80
Purchase #2	$185.72	5.183%	$195.3459	$195.35	$195.35	$195.30
Purchase #3	$79.31	7.326%	$85.1203	$85.12	$85.10	$85.10
Purchase #4	$217.53	8.406%	$235.8156	$235.82	$235.80	$235.80
Purchase #5	$172.82	7.383%	$185.5793	$185.58	$185.60	$185.60
Purchase #6	$17.81	9.548%	$19.5105	$19.51	$19.50	$19.50
Purchase #7	$29.99	7.194%	$32.1475	$32.15	$32.15	$32.10
7 purchase totals =	$785.49		$840.3002	$840.31	$840.30	$840.20