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	$137.25	5.243%	$144.446	$144.45	$144.45	$144.40
Purchase #2	$159.32	13.521%	$180.8617	$180.86	$180.85	$180.90
Purchase #3	$81.58	4.582%	$85.318	$85.32	$85.30	$85.30
Purchase #4	$99.83	13.120%	$112.9277	$112.93	$112.95	$112.90
Purchase #5	$249.93	7.213%	$267.9575	$267.96	$267.95	$268.00
Purchase #6	$64.91	9.745%	$71.2355	$71.24	$71.25	$71.20
Purchase #7	$73.82	3.139%	$76.1372	$76.14	$76.15	$76.10
7 purchase totals =	$866.64		$938.8836	$938.90	$938.90	$938.80