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	$71.83	12.818%	$81.0372	$81.04	$81.05	$81.00
Purchase #2	$185.66	5.814%	$196.4543	$196.45	$196.45	$196.50
Purchase #3	$25.45	8.502%	$27.6138	$27.61	$27.60	$27.60
Purchase #4	$84.82	11.132%	$94.2622	$94.26	$94.25	$94.30
Purchase #5	$58.68	4.430%	$61.2795	$61.28	$61.30	$61.30
Purchase #6	$180.58	3.795%	$187.433	$187.43	$187.45	$187.40
Purchase #7	$170.29	8.197%	$184.2487	$184.25	$184.25	$184.20
7 purchase totals =	$777.31		$832.3287	$832.32	$832.35	$832.30