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	$44.54	5.562%	$47.0173	$47.02	$47.00	$47.00
Purchase #2	$171.29	11.280%	$190.6115	$190.61	$190.60	$190.60
Purchase #3	$162.68	13.190%	$184.1375	$184.14	$184.15	$184.10
Purchase #4	$79.88	11.538%	$89.0966	$89.10	$89.10	$89.10
Purchase #5	$40.46	4.794%	$42.3997	$42.40	$42.40	$42.40
Purchase #6	$16.36	13.109%	$18.5046	$18.50	$18.50	$18.50
Purchase #7	$243.62	7.170%	$261.0876	$261.09	$261.10	$261.10
7 purchase totals =	$758.83		$832.8548	$832.86	$832.85	$832.80