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	$72.47	8.488%	$78.6213	$78.62	$78.60	$78.60
Purchase #2	$222.64	11.643%	$248.562	$248.56	$248.55	$248.60
Purchase #3	$174.45	11.229%	$194.039	$194.04	$194.05	$194.00
Purchase #4	$230.54	3.629%	$238.9063	$238.91	$238.90	$238.90
Purchase #5	$139.65	5.581%	$147.4439	$147.44	$147.45	$147.40
Purchase #6	$13.30	9.571%	$14.5729	$14.57	$14.55	$14.60
Purchase #7	$248.83	8.112%	$269.0151	$269.02	$269.00	$269.00
7 purchase totals =	$1,101.88		$1,191.1605	$1,191.16	$1,191.10	$1,191.10