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	$90.70	10.369%	$100.1047	$100.10	$100.10	$100.10
Purchase #2	$41.75	8.275%	$45.2048	$45.20	$45.20	$45.20
Purchase #3	$54.93	5.424%	$57.9094	$57.91	$57.90	$57.90
Purchase #4	$61.56	10.265%	$67.8791	$67.88	$67.90	$67.90
Purchase #5	$169.30	5.242%	$178.1747	$178.17	$178.15	$178.20
Purchase #6	$54.50	9.681%	$59.7761	$59.78	$59.80	$59.80
Purchase #7	$27.55	4.394%	$28.7605	$28.76	$28.75	$28.80
7 purchase totals =	$500.29		$537.8093	$537.80	$537.80	$537.90