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	$100.88	8.360%	$109.3136	$109.31	$109.30	$109.30
Purchase #2	$151.37	11.618%	$168.9562	$168.96	$168.95	$169.00
Purchase #3	$131.70	10.293%	$145.2559	$145.26	$145.25	$145.30
Purchase #4	$176.54	11.873%	$197.5006	$197.50	$197.50	$197.50
Purchase #5	$192.46	6.109%	$204.2174	$204.22	$204.20	$204.20
Purchase #6	$140.81	7.637%	$151.5637	$151.56	$151.55	$151.60
Purchase #7	$37.67	6.867%	$40.2568	$40.26	$40.25	$40.30
7 purchase totals =	$931.43		$1,017.0642	$1,017.07	$1,017.00	$1,017.20