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	$47.82	13.314%	$54.1868	$54.19	$54.20	$54.20
Purchase #2	$113.81	8.174%	$123.1128	$123.11	$123.10	$123.10
Purchase #3	$88.83	13.108%	$100.4738	$100.47	$100.45	$100.50
Purchase #4	$221.76	4.179%	$231.0274	$231.03	$231.05	$231.00
Purchase #5	$60.98	3.687%	$63.2283	$63.23	$63.25	$63.20
Purchase #6	$221.79	9.754%	$243.4234	$243.42	$243.40	$243.40
Purchase #7	$241.88	11.131%	$268.8037	$268.80	$268.80	$268.80
7 purchase totals =	$996.87		$1,084.2562	$1,084.25	$1,084.25	$1,084.20