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	$70.28	10.301%	$77.5195	$77.52	$77.50	$77.50
Purchase #2	$131.90	9.834%	$144.871	$144.87	$144.85	$144.90
Purchase #3	$89.72	7.317%	$96.2848	$96.28	$96.30	$96.30
Purchase #4	$128.39	12.201%	$144.0549	$144.05	$144.05	$144.10
Purchase #5	$90.31	13.268%	$102.2923	$102.29	$102.30	$102.30
Purchase #6	$174.57	9.306%	$190.8155	$190.82	$190.80	$190.80
Purchase #7	$54.93	13.869%	$62.5482	$62.55	$62.55	$62.50
7 purchase totals =	$740.10		$818.3862	$818.38	$818.35	$818.40