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	$85.66	6.394%	$91.1371	$91.14	$91.15	$91.10
Purchase #2	$38.33	7.864%	$41.3443	$41.34	$41.35	$41.30
Purchase #3	$39.86	5.144%	$41.9104	$41.91	$41.90	$41.90
Purchase #4	$183.28	8.528%	$198.9101	$198.91	$198.90	$198.90
Purchase #5	$54.75	5.782%	$57.9156	$57.92	$57.90	$57.90
Purchase #6	$47.83	11.825%	$53.4859	$53.49	$53.50	$53.50
Purchase #7	$67.69	8.280%	$73.2947	$73.29	$73.30	$73.30
7 purchase totals =	$517.40		$557.9981	$558.00	$558.00	$557.90