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	$39.92	5.800%	$42.2354	$42.24	$42.25	$42.20
Purchase #2	$55.93	9.854%	$61.4413	$61.44	$61.45	$61.40
Purchase #3	$114.27	6.709%	$121.9364	$121.94	$121.95	$121.90
Purchase #4	$80.94	6.713%	$86.3735	$86.37	$86.35	$86.40
Purchase #5	$41.94	7.457%	$45.0675	$45.07	$45.05	$45.10
Purchase #6	$14.66	10.862%	$16.2524	$16.25	$16.25	$16.30
Purchase #7	$145.32	13.630%	$165.1271	$165.13	$165.15	$165.10
7 purchase totals =	$492.98		$538.4336	$538.44	$538.45	$538.40