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	$99.64	10.260%	$109.8631	$109.86	$109.85	$109.90
Purchase #2	$81.26	8.717%	$88.3434	$88.34	$88.35	$88.30
Purchase #3	$78.41	6.819%	$83.7568	$83.76	$83.75	$83.80
Purchase #4	$166.28	6.138%	$176.4863	$176.49	$176.50	$176.50
Purchase #5	$33.52	6.321%	$35.6388	$35.64	$35.65	$35.60
Purchase #6	$29.40	10.605%	$32.5179	$32.52	$32.50	$32.50
Purchase #7	$225.90	7.795%	$243.5089	$243.51	$243.50	$243.50
7 purchase totals =	$714.41		$770.1152	$770.12	$770.10	$770.10