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	$127.63	4.109%	$132.8743	$132.87	$132.85	$132.90
Purchase #2	$78.84	8.610%	$85.6281	$85.63	$85.65	$85.60
Purchase #3	$222.25	9.343%	$243.0148	$243.01	$243.00	$243.00
Purchase #4	$135.80	5.167%	$142.8168	$142.82	$142.80	$142.80
Purchase #5	$78.62	13.139%	$88.9499	$88.95	$88.95	$88.90
Purchase #6	$243.96	6.536%	$259.9052	$259.91	$259.90	$259.90
Purchase #7	$222.80	10.498%	$246.1895	$246.19	$246.20	$246.20
7 purchase totals =	$1,109.90		$1,199.3786	$1,199.38	$1,199.35	$1,199.30