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	$78.40	4.404%	$81.8527	$81.85	$81.85	$81.90
Purchase #2	$218.33	12.204%	$244.975	$244.98	$245.00	$245.00
Purchase #3	$64.29	5.107%	$67.5733	$67.57	$67.55	$67.60
Purchase #4	$20.86	5.856%	$22.0816	$22.08	$22.10	$22.10
Purchase #5	$72.66	11.814%	$81.2441	$81.24	$81.25	$81.20
Purchase #6	$89.69	10.496%	$99.1039	$99.10	$99.10	$99.10
Purchase #7	$197.78	8.865%	$215.3132	$215.31	$215.30	$215.30
7 purchase totals =	$742.01		$812.1438	$812.13	$812.15	$812.20