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	$172.30	9.120%	$188.0138	$188.01	$188.00	$188.00
Purchase #2	$99.86	5.531%	$105.3833	$105.38	$105.40	$105.40
Purchase #3	$172.86	4.232%	$180.1754	$180.18	$180.20	$180.20
Purchase #4	$140.38	12.714%	$158.2279	$158.23	$158.25	$158.20
Purchase #5	$233.69	13.126%	$264.3641	$264.36	$264.35	$264.40
Purchase #6	$26.33	9.349%	$28.7916	$28.79	$28.80	$28.80
Purchase #7	$162.51	13.741%	$184.8405	$184.84	$184.85	$184.80
7 purchase totals =	$1,007.93		$1,109.7966	$1,109.79	$1,109.85	$1,109.80