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	$110.68	7.370%	$118.8371	$118.84	$118.85	$118.80
Purchase #2	$82.54	9.202%	$90.1353	$90.14	$90.15	$90.10
Purchase #3	$175.61	7.603%	$188.9616	$188.96	$188.95	$189.00
Purchase #4	$161.64	4.314%	$168.6131	$168.61	$168.60	$168.60
Purchase #5	$78.62	13.756%	$89.435	$89.44	$89.45	$89.40
Purchase #6	$162.88	4.224%	$169.7601	$169.76	$169.75	$169.80
Purchase #7	$8.94	12.181%	$10.029	$10.03	$10.05	$10.00
7 purchase totals =	$780.91		$835.7712	$835.78	$835.80	$835.70