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	$37.50	11.755%	$41.9081	$41.91	$41.90	$41.90
Purchase #2	$171.70	4.456%	$179.351	$179.35	$179.35	$179.40
Purchase #3	$208.57	7.711%	$224.6528	$224.65	$224.65	$224.70
Purchase #4	$137.57	4.281%	$143.4594	$143.46	$143.45	$143.50
Purchase #5	$185.69	13.220%	$210.2382	$210.24	$210.25	$210.20
Purchase #6	$59.28	12.230%	$66.5299	$66.53	$66.55	$66.50
Purchase #7	$209.36	9.703%	$229.6742	$229.67	$229.65	$229.70
7 purchase totals =	$1,009.67		$1,095.8136	$1,095.81	$1,095.80	$1,095.90