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	$183.43	3.655%	$190.1344	$190.13	$190.15	$190.10
Purchase #2	$29.60	3.114%	$30.5217	$30.52	$30.50	$30.50
Purchase #3	$203.31	9.171%	$221.9556	$221.96	$221.95	$222.00
Purchase #4	$40.54	6.616%	$43.2221	$43.22	$43.20	$43.20
Purchase #5	$35.84	12.713%	$40.3963	$40.40	$40.40	$40.40
Purchase #6	$183.52	11.867%	$205.2983	$205.30	$205.30	$205.30
Purchase #7	$115.39	10.148%	$127.0998	$127.10	$127.10	$127.10
7 purchase totals =	$791.63		$858.6282	$858.63	$858.60	$858.60