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	$67.38	3.237%	$69.5611	$69.56	$69.55	$69.60
Purchase #2	$146.67	13.673%	$166.7242	$166.72	$166.70	$166.70
Purchase #3	$67.72	9.655%	$74.2584	$74.26	$74.25	$74.30
Purchase #4	$174.37	12.532%	$196.222	$196.22	$196.20	$196.20
Purchase #5	$225.32	6.473%	$239.905	$239.91	$239.90	$239.90
Purchase #6	$78.38	12.771%	$88.3899	$88.39	$88.40	$88.40
Purchase #7	$171.59	13.654%	$195.0189	$195.02	$195.00	$195.00
7 purchase totals =	$931.43		$1,030.0795	$1,030.08	$1,030.00	$1,030.10