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	$126.48	9.483%	$138.4741	$138.47	$138.45	$138.50
Purchase #2	$179.94	5.474%	$189.7899	$189.79	$189.80	$189.80
Purchase #3	$209.32	11.611%	$233.6241	$233.62	$233.60	$233.60
Purchase #4	$94.57	5.672%	$99.934	$99.93	$99.95	$99.90
Purchase #5	$216.42	12.807%	$244.1369	$244.14	$244.15	$244.10
Purchase #6	$127.76	12.254%	$143.4157	$143.42	$143.40	$143.40
Purchase #7	$46.46	11.680%	$51.8865	$51.89	$51.90	$51.90
7 purchase totals =	$1,000.95		$1,101.2612	$1,101.26	$1,101.25	$1,101.20