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	$54.59	9.342%	$59.6898	$59.69	$59.70	$59.70
Purchase #2	$126.34	9.504%	$138.3474	$138.35	$138.35	$138.30
Purchase #3	$40.27	4.834%	$42.2167	$42.22	$42.20	$42.20
Purchase #4	$84.33	4.120%	$87.8044	$87.80	$87.80	$87.80
Purchase #5	$178.73	11.770%	$199.7665	$199.77	$199.75	$199.80
Purchase #6	$123.40	6.174%	$131.0187	$131.02	$131.00	$131.00
Purchase #7	$156.70	4.780%	$164.1903	$164.19	$164.20	$164.20
7 purchase totals =	$764.36		$823.0338	$823.04	$823.00	$823.00