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	$171.86	5.250%	$180.8827	$180.88	$180.90	$180.90
Purchase #2	$70.51	4.113%	$73.4101	$73.41	$73.40	$73.40
Purchase #3	$82.71	10.127%	$91.086	$91.09	$91.10	$91.10
Purchase #4	$169.54	5.338%	$178.59	$178.59	$178.60	$178.60
Purchase #5	$9.96	6.284%	$10.5859	$10.59	$10.60	$10.60
Purchase #6	$196.69	11.260%	$218.8373	$218.84	$218.85	$218.80
Purchase #7	$163.73	11.558%	$182.6539	$182.65	$182.65	$182.70
7 purchase totals =	$865.00		$936.0459	$936.05	$936.10	$936.10