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	$178.90	12.204%	$200.733	$200.73	$200.75	$200.70
Purchase #2	$40.82	7.219%	$43.7668	$43.77	$43.75	$43.80
Purchase #3	$7.55	6.332%	$8.0281	$8.03	$8.05	$8.00
Purchase #4	$103.84	3.398%	$107.3685	$107.37	$107.35	$107.40
Purchase #5	$118.97	10.399%	$131.3417	$131.34	$131.35	$131.30
Purchase #6	$209.75	6.112%	$222.5699	$222.57	$222.55	$222.60
Purchase #7	$127.60	13.242%	$144.4968	$144.50	$144.50	$144.50
7 purchase totals =	$787.43		$858.3048	$858.31	$858.30	$858.30