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	$134.85	5.315%	$142.0173	$142.02	$142.00	$142.00
Purchase #2	$49.39	10.610%	$54.6303	$54.63	$54.65	$54.60
Purchase #3	$115.60	13.353%	$131.0361	$131.04	$131.05	$131.00
Purchase #4	$42.46	8.537%	$46.0848	$46.08	$46.10	$46.10
Purchase #5	$56.59	8.646%	$61.4828	$61.48	$61.50	$61.50
Purchase #6	$238.71	6.229%	$253.5792	$253.58	$253.60	$253.60
Purchase #7	$172.26	6.320%	$183.1468	$183.15	$183.15	$183.10
7 purchase totals =	$809.86		$871.9773	$871.98	$872.05	$871.90