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	$76.40	9.514%	$83.6687	$83.67	$83.65	$83.70
Purchase #2	$152.72	9.784%	$167.6621	$167.66	$167.65	$167.70
Purchase #3	$249.65	13.414%	$283.1381	$283.14	$283.15	$283.10
Purchase #4	$234.59	6.300%	$249.3692	$249.37	$249.35	$249.40
Purchase #5	$108.59	4.822%	$113.8262	$113.83	$113.85	$113.80
Purchase #6	$64.73	7.866%	$69.8217	$69.82	$69.80	$69.80
Purchase #7	$36.46	12.171%	$40.8975	$40.90	$40.90	$40.90
7 purchase totals =	$923.14		$1,008.3835	$1,008.39	$1,008.35	$1,008.40