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	$235.57	13.343%	$267.0021	$267.00	$267.00	$267.00
Purchase #2	$192.91	3.516%	$199.6927	$199.69	$199.70	$199.70
Purchase #3	$59.34	10.823%	$65.7624	$65.76	$65.75	$65.80
Purchase #4	$214.77	13.743%	$244.2858	$244.29	$244.30	$244.30
Purchase #5	$82.27	4.297%	$85.8051	$85.81	$85.80	$85.80
Purchase #6	$28.50	3.562%	$29.5152	$29.52	$29.50	$29.50
Purchase #7	$79.56	12.858%	$89.7898	$89.79	$89.80	$89.80
7 purchase totals =	$892.92		$981.8531	$981.86	$981.85	$981.90