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	$28.37	10.717%	$31.4104	$31.41	$31.40	$31.40
Purchase #2	$133.25	13.418%	$151.1295	$151.13	$151.15	$151.10
Purchase #3	$95.64	5.165%	$100.5798	$100.58	$100.60	$100.60
Purchase #4	$198.55	7.676%	$213.7907	$213.79	$213.80	$213.80
Purchase #5	$226.26	6.314%	$240.5461	$240.55	$240.55	$240.50
Purchase #6	$71.44	11.408%	$79.5899	$79.59	$79.60	$79.60
Purchase #7	$91.43	6.708%	$97.5631	$97.56	$97.55	$97.60
7 purchase totals =	$844.94		$914.6095	$914.61	$914.65	$914.60