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	$78.86	5.445%	$83.1539	$83.15	$83.15	$83.20
Purchase #2	$225.65	3.852%	$234.342	$234.34	$234.35	$234.30
Purchase #3	$225.51	12.332%	$253.3199	$253.32	$253.30	$253.30
Purchase #4	$35.98	13.653%	$40.8923	$40.89	$40.90	$40.90
Purchase #5	$69.42	8.562%	$75.3637	$75.36	$75.35	$75.40
Purchase #6	$129.38	7.689%	$139.328	$139.33	$139.35	$139.30
Purchase #7	$137.43	3.718%	$142.5396	$142.54	$142.55	$142.50
7 purchase totals =	$902.23		$968.9394	$968.93	$968.95	$968.90