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	$167.56	10.740%	$185.5559	$185.56	$185.55	$185.60
Purchase #2	$180.55	10.209%	$198.9823	$198.98	$199.00	$199.00
Purchase #3	$83.66	6.301%	$88.9314	$88.93	$88.95	$88.90
Purchase #4	$105.76	4.422%	$110.4367	$110.44	$110.45	$110.40
Purchase #5	$239.77	4.493%	$250.5429	$250.54	$250.55	$250.50
Purchase #6	$81.38	9.240%	$88.8995	$88.90	$88.90	$88.90
Purchase #7	$83.88	13.844%	$95.4923	$95.49	$95.50	$95.50
7 purchase totals =	$942.56		$1,018.8410	$1,018.84	$1,018.90	$1,018.80