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	$35.38	5.105%	$37.1861	$37.19	$37.20	$37.20
Purchase #2	$172.84	10.541%	$191.0591	$191.06	$191.05	$191.10
Purchase #3	$47.63	7.683%	$51.2894	$51.29	$51.30	$51.30
Purchase #4	$115.73	11.353%	$128.8688	$128.87	$128.85	$128.90
Purchase #5	$123.30	5.678%	$130.301	$130.30	$130.30	$130.30
Purchase #6	$59.56	4.316%	$62.1306	$62.13	$62.15	$62.10
Purchase #7	$174.97	7.655%	$188.364	$188.36	$188.35	$188.40
7 purchase totals =	$729.41		$789.1990	$789.20	$789.20	$789.30