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	$173.91	5.740%	$183.8924	$183.89	$183.90	$183.90
Purchase #2	$116.79	9.813%	$128.2506	$128.25	$128.25	$128.30
Purchase #3	$193.89	9.567%	$212.4395	$212.44	$212.45	$212.40
Purchase #4	$90.60	9.443%	$99.1554	$99.16	$99.15	$99.20
Purchase #5	$161.45	4.232%	$168.2826	$168.28	$168.30	$168.30
Purchase #6	$199.66	11.124%	$221.8702	$221.87	$221.85	$221.90
Purchase #7	$69.65	4.228%	$72.5948	$72.59	$72.60	$72.60
7 purchase totals =	$1,005.95		$1,086.4855	$1,086.48	$1,086.50	$1,086.60