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	$51.72	4.576%	$54.0867	$54.09	$54.10	$54.10
Purchase #2	$36.89	8.188%	$39.9106	$39.91	$39.90	$39.90
Purchase #3	$155.73	3.729%	$161.5372	$161.54	$161.55	$161.50
Purchase #4	$56.60	4.365%	$59.0706	$59.07	$59.05	$59.10
Purchase #5	$134.62	9.703%	$147.6822	$147.68	$147.70	$147.70
Purchase #6	$179.45	3.824%	$186.3122	$186.31	$186.30	$186.30
Purchase #7	$96.37	3.722%	$99.9569	$99.96	$99.95	$100.00
7 purchase totals =	$711.38		$748.5564	$748.56	$748.55	$748.60