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	$80.58	12.123%	$90.3487	$90.35	$90.35	$90.30
Purchase #2	$136.91	6.677%	$146.0515	$146.05	$146.05	$146.10
Purchase #3	$166.58	5.165%	$175.1839	$175.18	$175.20	$175.20
Purchase #4	$228.98	13.823%	$260.6319	$260.63	$260.65	$260.60
Purchase #5	$175.33	9.215%	$191.4867	$191.49	$191.50	$191.50
Purchase #6	$90.41	5.193%	$95.105	$95.11	$95.10	$95.10
Purchase #7	$39.69	13.660%	$45.1117	$45.11	$45.10	$45.10
7 purchase totals =	$918.48		$1,003.9194	$1,003.92	$1,003.95	$1,003.90