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	$170.56	9.568%	$186.8792	$186.88	$186.90	$186.90
Purchase #2	$38.78	6.222%	$41.1929	$41.19	$41.20	$41.20
Purchase #3	$212.83	4.500%	$222.4074	$222.41	$222.40	$222.40
Purchase #4	$209.39	5.682%	$221.2875	$221.29	$221.30	$221.30
Purchase #5	$152.89	13.143%	$172.9843	$172.98	$173.00	$173.00
Purchase #6	$211.39	10.442%	$233.4633	$233.46	$233.45	$233.50
Purchase #7	$97.44	3.317%	$100.6721	$100.67	$100.65	$100.70
7 purchase totals =	$1,093.28		$1,178.8867	$1,178.88	$1,178.90	$1,179.00