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	$80.56	11.665%	$89.9573	$89.96	$89.95	$90.00
Purchase #2	$141.50	5.829%	$149.748	$149.75	$149.75	$149.70
Purchase #3	$101.26	11.421%	$112.8249	$112.82	$112.80	$112.80
Purchase #4	$248.87	6.406%	$264.8126	$264.81	$264.80	$264.80
Purchase #5	$217.30	3.450%	$224.7969	$224.80	$224.80	$224.80
Purchase #6	$233.45	7.753%	$251.5494	$251.55	$251.55	$251.50
Purchase #7	$76.89	7.822%	$82.9043	$82.90	$82.90	$82.90
7 purchase totals =	$1,099.83		$1,176.5934	$1,176.59	$1,176.55	$1,176.50