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	$171.85	11.239%	$191.1642	$191.16	$191.15	$191.20
Purchase #2	$29.50	5.137%	$31.0154	$31.02	$31.00	$31.00
Purchase #3	$149.96	11.281%	$166.877	$166.88	$166.90	$166.90
Purchase #4	$6.52	12.616%	$7.3426	$7.34	$7.35	$7.30
Purchase #5	$154.36	5.671%	$163.1138	$163.11	$163.10	$163.10
Purchase #6	$152.35	10.175%	$167.8516	$167.85	$167.85	$167.90
Purchase #7	$101.31	3.694%	$105.0524	$105.05	$105.05	$105.10
7 purchase totals =	$765.85		$832.4170	$832.41	$832.40	$832.50