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	$85.63	8.280%	$92.7202	$92.72	$92.70	$92.70
Purchase #2	$106.45	3.279%	$109.9405	$109.94	$109.95	$109.90
Purchase #3	$18.83	9.592%	$20.6362	$20.64	$20.65	$20.60
Purchase #4	$191.73	6.344%	$203.8934	$203.89	$203.90	$203.90
Purchase #5	$6.90	3.189%	$7.12	$7.12	$7.10	$7.10
Purchase #6	$208.58	10.574%	$230.6352	$230.64	$230.65	$230.60
Purchase #7	$98.71	9.872%	$108.4547	$108.45	$108.45	$108.50
7 purchase totals =	$716.83		$773.4002	$773.40	$773.40	$773.30