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	$123.81	6.570%	$131.9443	$131.94	$131.95	$131.90
Purchase #2	$183.29	4.378%	$191.3144	$191.31	$191.30	$191.30
Purchase #3	$96.28	9.714%	$105.6326	$105.63	$105.65	$105.60
Purchase #4	$35.50	12.412%	$39.9063	$39.91	$39.90	$39.90
Purchase #5	$159.49	12.447%	$179.3417	$179.34	$179.35	$179.30
Purchase #6	$136.28	8.785%	$148.2522	$148.25	$148.25	$148.30
Purchase #7	$86.47	7.857%	$93.2639	$93.26	$93.25	$93.30
7 purchase totals =	$821.12		$889.6554	$889.64	$889.65	$889.60