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	$175.42	4.272%	$182.9139	$182.91	$182.90	$182.90
Purchase #2	$72.82	7.507%	$78.2866	$78.29	$78.30	$78.30
Purchase #3	$29.52	7.482%	$31.7287	$31.73	$31.75	$31.70
Purchase #4	$49.73	3.649%	$51.5446	$51.54	$51.55	$51.50
Purchase #5	$150.37	7.382%	$161.4703	$161.47	$161.45	$161.50
Purchase #6	$110.29	13.733%	$125.4361	$125.44	$125.45	$125.40
Purchase #7	$185.76	7.178%	$199.0939	$199.09	$199.10	$199.10
7 purchase totals =	$773.91		$830.4741	$830.47	$830.50	$830.40