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	$189.78	4.800%	$198.8894	$198.89	$198.90	$198.90
Purchase #2	$249.26	7.520%	$268.0044	$268.00	$268.00	$268.00
Purchase #3	$89.79	10.651%	$99.3535	$99.35	$99.35	$99.40
Purchase #4	$149.78	5.563%	$158.1123	$158.11	$158.10	$158.10
Purchase #5	$60.33	9.490%	$66.0553	$66.06	$66.05	$66.10
Purchase #6	$96.39	9.128%	$105.1885	$105.19	$105.20	$105.20
Purchase #7	$180.97	5.591%	$191.088	$191.09	$191.10	$191.10
7 purchase totals =	$1,016.30		$1,086.6914	$1,086.69	$1,086.70	$1,086.80