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	$175.39	5.817%	$185.5924	$185.59	$185.60	$185.60
Purchase #2	$33.80	13.458%	$38.3488	$38.35	$38.35	$38.30
Purchase #3	$73.48	8.699%	$79.872	$79.87	$79.85	$79.90
Purchase #4	$23.76	11.456%	$26.4819	$26.48	$26.50	$26.50
Purchase #5	$72.82	4.400%	$76.0241	$76.02	$76.00	$76.00
Purchase #6	$132.55	13.470%	$150.4045	$150.40	$150.40	$150.40
Purchase #7	$78.78	13.117%	$89.1136	$89.11	$89.10	$89.10
7 purchase totals =	$590.58		$645.8373	$645.82	$645.80	$645.80