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	$158.86	10.174%	$175.0224	$175.02	$175.00	$175.00
Purchase #2	$177.83	6.790%	$189.9047	$189.90	$189.90	$189.90
Purchase #3	$120.66	13.140%	$136.5147	$136.51	$136.50	$136.50
Purchase #4	$173.26	9.467%	$189.6625	$189.66	$189.65	$189.70
Purchase #5	$243.26	13.629%	$276.4139	$276.41	$276.40	$276.40
Purchase #6	$31.89	10.567%	$35.2598	$35.26	$35.25	$35.30
Purchase #7	$240.65	6.623%	$256.5882	$256.59	$256.60	$256.60
7 purchase totals =	$1,146.41		$1,259.3662	$1,259.35	$1,259.30	$1,259.40