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	$140.84	6.729%	$150.3171	$150.32	$150.30	$150.30
Purchase #2	$104.89	13.163%	$118.6967	$118.70	$118.70	$118.70
Purchase #3	$205.34	5.271%	$216.1635	$216.16	$216.15	$216.20
Purchase #4	$127.37	13.527%	$144.5993	$144.60	$144.60	$144.60
Purchase #5	$162.72	4.838%	$170.5924	$170.59	$170.60	$170.60
Purchase #6	$204.41	13.775%	$232.5675	$232.57	$232.55	$232.60
Purchase #7	$125.30	11.662%	$139.9125	$139.91	$139.90	$139.90
7 purchase totals =	$1,070.87		$1,172.8490	$1,172.85	$1,172.80	$1,172.90