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	$26.69	7.310%	$28.641	$28.64	$28.65	$28.60
Purchase #2	$20.26	10.201%	$22.3267	$22.33	$22.35	$22.30
Purchase #3	$185.25	8.382%	$200.7777	$200.78	$200.80	$200.80
Purchase #4	$141.96	10.141%	$156.3562	$156.36	$156.35	$156.40
Purchase #5	$39.26	7.749%	$42.3023	$42.30	$42.30	$42.30
Purchase #6	$196.86	13.131%	$222.7097	$222.71	$222.70	$222.70
Purchase #7	$23.82	6.816%	$25.4436	$25.44	$25.45	$25.40
7 purchase totals =	$634.10		$698.5572	$698.56	$698.60	$698.50