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	$37.89	12.194%	$42.5103	$42.51	$42.50	$42.50
Purchase #2	$61.70	9.640%	$67.6479	$67.65	$67.65	$67.60
Purchase #3	$250.82	13.803%	$285.4407	$285.44	$285.45	$285.40
Purchase #4	$79.87	8.656%	$86.7835	$86.78	$86.80	$86.80
Purchase #5	$237.43	9.245%	$259.3804	$259.38	$259.40	$259.40
Purchase #6	$156.40	12.260%	$175.5746	$175.57	$175.55	$175.60
Purchase #7	$210.92	7.212%	$226.1316	$226.13	$226.15	$226.10
7 purchase totals =	$1,035.03		$1,143.4690	$1,143.46	$1,143.50	$1,143.40