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	$39.79	13.865%	$45.3069	$45.31	$45.30	$45.30
Purchase #2	$104.38	5.806%	$110.4403	$110.44	$110.45	$110.40
Purchase #3	$209.25	8.278%	$226.5717	$226.57	$226.55	$226.60
Purchase #4	$145.88	6.559%	$155.4483	$155.45	$155.45	$155.40
Purchase #5	$56.86	5.314%	$59.8815	$59.88	$59.90	$59.90
Purchase #6	$146.42	4.413%	$152.8815	$152.88	$152.90	$152.90
Purchase #7	$121.36	8.702%	$131.9207	$131.92	$131.90	$131.90
7 purchase totals =	$823.94		$882.4509	$882.45	$882.45	$882.40