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	$223.97	7.316%	$240.3556	$240.36	$240.35	$240.40
Purchase #2	$40.27	12.600%	$45.344	$45.34	$45.35	$45.30
Purchase #3	$93.71	7.145%	$100.4056	$100.41	$100.40	$100.40
Purchase #4	$120.63	4.720%	$126.3237	$126.32	$126.30	$126.30
Purchase #5	$83.84	3.600%	$86.8582	$86.86	$86.85	$86.90
Purchase #6	$109.35	7.658%	$117.724	$117.72	$117.70	$117.70
Purchase #7	$161.33	7.529%	$173.4765	$173.48	$173.50	$173.50
7 purchase totals =	$833.10		$890.4876	$890.49	$890.45	$890.50