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	$83.91	4.444%	$87.639	$87.64	$87.65	$87.60
Purchase #2	$121.65	13.260%	$137.7808	$137.78	$137.80	$137.80
Purchase #3	$143.33	4.804%	$150.2156	$150.22	$150.20	$150.20
Purchase #4	$249.87	4.654%	$261.4989	$261.50	$261.50	$261.50
Purchase #5	$29.32	8.437%	$31.7937	$31.79	$31.80	$31.80
Purchase #6	$30.41	4.766%	$31.8593	$31.86	$31.85	$31.90
Purchase #7	$35.91	11.600%	$40.0756	$40.08	$40.10	$40.10
7 purchase totals =	$694.40		$740.8629	$740.87	$740.90	$740.90