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	$123.41	12.507%	$138.8449	$138.84	$138.85	$138.80
Purchase #2	$161.31	3.600%	$167.1172	$167.12	$167.10	$167.10
Purchase #3	$89.25	12.127%	$100.0733	$100.07	$100.05	$100.10
Purchase #4	$225.86	6.489%	$240.5161	$240.52	$240.50	$240.50
Purchase #5	$144.42	12.582%	$162.5909	$162.59	$162.60	$162.60
Purchase #6	$37.65	3.796%	$39.0792	$39.08	$39.10	$39.10
Purchase #7	$38.48	3.871%	$39.9696	$39.97	$39.95	$40.00
7 purchase totals =	$820.38		$888.1912	$888.19	$888.15	$888.20