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	$190.73	3.236%	$196.902	$196.90	$196.90	$196.90
Purchase #2	$157.65	11.400%	$175.6221	$175.62	$175.60	$175.60
Purchase #3	$124.83	9.161%	$136.2657	$136.27	$136.25	$136.30
Purchase #4	$174.98	3.231%	$180.6336	$180.63	$180.65	$180.60
Purchase #5	$131.30	5.868%	$139.0047	$139.00	$139.00	$139.00
Purchase #6	$13.28	4.229%	$13.8416	$13.84	$13.85	$13.80
Purchase #7	$91.44	8.721%	$99.4145	$99.41	$99.40	$99.40
7 purchase totals =	$884.21		$941.6842	$941.67	$941.65	$941.60