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	$100.26	8.821%	$109.1039	$109.10	$109.10	$109.10
Purchase #2	$86.37	3.425%	$89.3282	$89.33	$89.35	$89.30
Purchase #3	$225.32	4.196%	$234.7744	$234.77	$234.75	$234.80
Purchase #4	$38.81	12.453%	$43.643	$43.64	$43.65	$43.60
Purchase #5	$168.88	11.471%	$188.2522	$188.25	$188.25	$188.30
Purchase #6	$98.28	7.861%	$106.0058	$106.01	$106.00	$106.00
Purchase #7	$67.44	7.826%	$72.7179	$72.72	$72.70	$72.70
7 purchase totals =	$785.36		$843.8254	$843.82	$843.80	$843.80