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	$89.88	8.110%	$97.1693	$97.17	$97.15	$97.20
Purchase #2	$208.91	9.339%	$228.4201	$228.42	$228.40	$228.40
Purchase #3	$216.47	6.780%	$231.1467	$231.15	$231.15	$231.10
Purchase #4	$83.98	6.266%	$89.2422	$89.24	$89.25	$89.20
Purchase #5	$128.64	8.696%	$139.8265	$139.83	$139.85	$139.80
Purchase #6	$206.46	9.128%	$225.3057	$225.31	$225.30	$225.30
Purchase #7	$155.60	12.819%	$175.5464	$175.55	$175.55	$175.50
7 purchase totals =	$1,089.94		$1,186.6569	$1,186.67	$1,186.65	$1,186.50