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	$19.78	3.324%	$20.4375	$20.44	$20.45	$20.40
Purchase #2	$88.26	12.750%	$99.5132	$99.51	$99.50	$99.50
Purchase #3	$117.81	4.502%	$123.1138	$123.11	$123.10	$123.10
Purchase #4	$153.79	11.242%	$171.0791	$171.08	$171.10	$171.10
Purchase #5	$113.34	6.245%	$120.4181	$120.42	$120.40	$120.40
Purchase #6	$147.95	13.482%	$167.8966	$167.90	$167.90	$167.90
Purchase #7	$61.42	12.844%	$69.3088	$69.31	$69.30	$69.30
7 purchase totals =	$702.35		$771.7671	$771.77	$771.75	$771.70