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	$25.36	11.656%	$28.316	$28.32	$28.30	$28.30
Purchase #2	$169.74	6.466%	$180.7154	$180.72	$180.70	$180.70
Purchase #3	$117.59	7.105%	$125.9448	$125.94	$125.95	$125.90
Purchase #4	$123.34	12.198%	$138.385	$138.39	$138.40	$138.40
Purchase #5	$67.96	4.702%	$71.1555	$71.16	$71.15	$71.20
Purchase #6	$90.48	5.393%	$95.3596	$95.36	$95.35	$95.40
Purchase #7	$166.43	11.721%	$185.9373	$185.94	$185.95	$185.90
7 purchase totals =	$760.90		$825.8136	$825.83	$825.80	$825.80