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	$64.82	3.524%	$67.1043	$67.10	$67.10	$67.10
Purchase #2	$93.76	6.837%	$100.1704	$100.17	$100.15	$100.20
Purchase #3	$221.55	3.250%	$228.7504	$228.75	$228.75	$228.80
Purchase #4	$133.35	7.808%	$143.762	$143.76	$143.75	$143.80
Purchase #5	$152.46	3.505%	$157.8037	$157.80	$157.80	$157.80
Purchase #6	$94.81	6.272%	$100.7565	$100.76	$100.75	$100.80
Purchase #7	$28.63	13.718%	$32.5575	$32.56	$32.55	$32.60
7 purchase totals =	$789.38		$830.9048	$830.90	$830.85	$831.10