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	$176.63	7.255%	$189.4445	$189.44	$189.45	$189.40
Purchase #2	$120.33	9.136%	$131.3233	$131.32	$131.30	$131.30
Purchase #3	$91.50	12.141%	$102.609	$102.61	$102.60	$102.60
Purchase #4	$6.84	9.143%	$7.4654	$7.47	$7.45	$7.50
Purchase #5	$145.88	8.390%	$158.1193	$158.12	$158.10	$158.10
Purchase #6	$35.69	4.620%	$37.3389	$37.34	$37.35	$37.30
Purchase #7	$108.37	6.447%	$115.3566	$115.36	$115.35	$115.40
7 purchase totals =	$685.24		$741.6570	$741.66	$741.60	$741.60