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	$96.81	4.247%	$100.9215	$100.92	$100.90	$100.90
Purchase #2	$159.62	13.690%	$181.472	$181.47	$181.45	$181.50
Purchase #3	$243.48	10.133%	$268.1518	$268.15	$268.15	$268.20
Purchase #4	$185.52	4.812%	$194.4472	$194.45	$194.45	$194.40
Purchase #5	$182.83	4.154%	$190.4248	$190.42	$190.40	$190.40
Purchase #6	$72.92	9.467%	$79.8233	$79.82	$79.80	$79.80
Purchase #7	$164.92	6.357%	$175.404	$175.40	$175.40	$175.40
7 purchase totals =	$1,106.10		$1,190.6446	$1,190.63	$1,190.55	$1,190.60