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	$129.82	9.223%	$141.7933	$141.79	$141.80	$141.80
Purchase #2	$96.89	3.261%	$100.0496	$100.05	$100.05	$100.00
Purchase #3	$33.87	3.790%	$35.1537	$35.15	$35.15	$35.20
Purchase #4	$179.76	5.761%	$190.116	$190.12	$190.10	$190.10
Purchase #5	$128.50	7.245%	$137.8098	$137.81	$137.80	$137.80
Purchase #6	$99.69	4.302%	$103.9787	$103.98	$104.00	$104.00
Purchase #7	$206.62	11.134%	$229.6251	$229.63	$229.65	$229.60
7 purchase totals =	$875.15		$938.5262	$938.53	$938.55	$938.50