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	$40.86	5.647%	$43.1674	$43.17	$43.15	$43.20
Purchase #2	$32.42	10.146%	$35.7093	$35.71	$35.70	$35.70
Purchase #3	$223.83	3.756%	$232.2371	$232.24	$232.25	$232.20
Purchase #4	$62.95	13.742%	$71.6006	$71.60	$71.60	$71.60
Purchase #5	$87.64	10.253%	$96.6257	$96.63	$96.65	$96.60
Purchase #6	$178.55	5.664%	$188.6631	$188.66	$188.65	$188.70
Purchase #7	$139.48	9.565%	$152.8213	$152.82	$152.80	$152.80
7 purchase totals =	$765.73		$820.8245	$820.83	$820.80	$820.80