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	$82.43	12.706%	$92.9036	$92.90	$92.90	$92.90
Purchase #2	$151.39	3.205%	$156.242	$156.24	$156.25	$156.20
Purchase #3	$204.44	10.215%	$225.3235	$225.32	$225.30	$225.30
Purchase #4	$41.56	12.295%	$46.6698	$46.67	$46.65	$46.70
Purchase #5	$215.56	12.600%	$242.7206	$242.72	$242.70	$242.70
Purchase #6	$124.75	5.312%	$131.3767	$131.38	$131.40	$131.40
Purchase #7	$165.78	6.601%	$176.7231	$176.72	$176.70	$176.70
7 purchase totals =	$985.91		$1,071.9593	$1,071.95	$1,071.90	$1,071.90