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	$81.25	11.584%	$90.662	$90.66	$90.65	$90.70
Purchase #2	$140.65	3.282%	$145.2661	$145.27	$145.25	$145.30
Purchase #3	$200.91	5.500%	$211.9601	$211.96	$211.95	$212.00
Purchase #4	$147.83	9.614%	$162.0424	$162.04	$162.05	$162.00
Purchase #5	$58.31	12.265%	$65.4617	$65.46	$65.45	$65.50
Purchase #6	$101.73	5.351%	$107.1736	$107.17	$107.15	$107.20
Purchase #7	$47.74	9.528%	$52.2887	$52.29	$52.30	$52.30
7 purchase totals =	$778.42		$834.8546	$834.85	$834.80	$835.00