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	$84.26	8.173%	$91.1466	$91.15	$91.15	$91.10
Purchase #2	$145.41	7.524%	$156.3506	$156.35	$156.35	$156.40
Purchase #3	$231.52	8.212%	$250.5324	$250.53	$250.55	$250.50
Purchase #4	$146.56	6.630%	$156.2769	$156.28	$156.30	$156.30
Purchase #5	$85.41	5.568%	$90.1656	$90.17	$90.15	$90.20
Purchase #6	$13.55	8.623%	$14.7184	$14.72	$14.70	$14.70
Purchase #7	$91.90	5.295%	$96.7661	$96.77	$96.75	$96.80
7 purchase totals =	$798.61		$855.9566	$855.97	$855.95	$856.00