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	$233.91	6.657%	$249.4814	$249.48	$249.50	$249.50
Purchase #2	$52.54	6.171%	$55.7822	$55.78	$55.80	$55.80
Purchase #3	$186.32	6.446%	$198.3302	$198.33	$198.35	$198.30
Purchase #4	$52.85	5.779%	$55.9042	$55.90	$55.90	$55.90
Purchase #5	$61.34	9.286%	$67.036	$67.04	$67.05	$67.00
Purchase #6	$123.86	9.283%	$135.3579	$135.36	$135.35	$135.40
Purchase #7	$144.43	5.666%	$152.6134	$152.61	$152.60	$152.60
7 purchase totals =	$855.25		$914.5053	$914.50	$914.55	$914.50