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	$40.82	3.617%	$42.2965	$42.30	$42.30	$42.30
Purchase #2	$116.70	8.720%	$126.8762	$126.88	$126.90	$126.90
Purchase #3	$91.95	8.732%	$99.9791	$99.98	$100.00	$100.00
Purchase #4	$152.67	12.106%	$171.1522	$171.15	$171.15	$171.20
Purchase #5	$120.75	12.867%	$136.2869	$136.29	$136.30	$136.30
Purchase #6	$164.50	4.164%	$171.3498	$171.35	$171.35	$171.30
Purchase #7	$185.90	6.279%	$197.5727	$197.57	$197.55	$197.60
7 purchase totals =	$873.29		$945.5134	$945.52	$945.55	$945.60