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	$161.76	13.787%	$184.0619	$184.06	$184.05	$184.10
Purchase #2	$134.82	6.362%	$143.3972	$143.40	$143.40	$143.40
Purchase #3	$81.42	4.850%	$85.3689	$85.37	$85.35	$85.40
Purchase #4	$72.45	4.713%	$75.8646	$75.86	$75.85	$75.90
Purchase #5	$168.62	10.185%	$185.7939	$185.79	$185.80	$185.80
Purchase #6	$122.78	4.501%	$128.3063	$128.31	$128.30	$128.30
Purchase #7	$42.73	8.729%	$46.4599	$46.46	$46.45	$46.50
7 purchase totals =	$784.58		$849.2527	$849.25	$849.20	$849.40