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	$227.52	5.527%	$240.095	$240.10	$240.10	$240.10
Purchase #2	$100.96	12.851%	$113.9344	$113.93	$113.95	$113.90
Purchase #3	$205.98	13.560%	$233.9109	$233.91	$233.90	$233.90
Purchase #4	$33.25	12.626%	$37.4481	$37.45	$37.45	$37.40
Purchase #5	$235.45	3.488%	$243.6625	$243.66	$243.65	$243.70
Purchase #6	$106.49	12.739%	$120.0558	$120.06	$120.05	$120.10
Purchase #7	$101.25	9.795%	$111.1674	$111.17	$111.15	$111.20
7 purchase totals =	$1,010.90		$1,100.2741	$1,100.28	$1,100.25	$1,100.30