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	$35.66	6.374%	$37.933	$37.93	$37.95	$37.90
Purchase #2	$174.83	3.793%	$181.4613	$181.46	$181.45	$181.50
Purchase #3	$49.76	7.560%	$53.5219	$53.52	$53.50	$53.50
Purchase #4	$49.34	12.208%	$55.3634	$55.36	$55.35	$55.40
Purchase #5	$166.40	11.330%	$185.2531	$185.25	$185.25	$185.30
Purchase #6	$51.65	7.770%	$55.6632	$55.66	$55.65	$55.70
Purchase #7	$62.65	8.630%	$68.0567	$68.06	$68.05	$68.10
7 purchase totals =	$590.29		$637.2526	$637.24	$637.20	$637.40