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	$145.63	3.216%	$150.3135	$150.31	$150.30	$150.30
Purchase #2	$57.42	3.575%	$59.4728	$59.47	$59.45	$59.50
Purchase #3	$18.52	12.198%	$20.7791	$20.78	$20.80	$20.80
Purchase #4	$226.38	4.490%	$236.5445	$236.54	$236.55	$236.50
Purchase #5	$120.47	6.597%	$128.4174	$128.42	$128.40	$128.40
Purchase #6	$101.34	3.583%	$104.971	$104.97	$104.95	$105.00
Purchase #7	$125.44	9.816%	$137.7532	$137.75	$137.75	$137.80
7 purchase totals =	$795.20		$838.2515	$838.24	$838.20	$838.30