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	$36.92	3.711%	$38.2901	$38.29	$38.30	$38.30
Purchase #2	$250.55	13.610%	$284.6499	$284.65	$284.65	$284.60
Purchase #3	$69.73	11.695%	$77.8849	$77.88	$77.90	$77.90
Purchase #4	$12.46	6.542%	$13.2751	$13.28	$13.30	$13.30
Purchase #5	$75.89	3.417%	$78.4832	$78.48	$78.50	$78.50
Purchase #6	$111.84	13.483%	$126.9194	$126.92	$126.90	$126.90
Purchase #7	$178.49	12.235%	$200.3283	$200.33	$200.35	$200.30
7 purchase totals =	$735.88		$819.8309	$819.83	$819.90	$819.80