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	$38.73	9.315%	$42.3377	$42.34	$42.35	$42.30
Purchase #2	$110.33	12.302%	$123.9028	$123.90	$123.90	$123.90
Purchase #3	$28.77	9.631%	$31.5408	$31.54	$31.55	$31.50
Purchase #4	$76.91	6.828%	$82.1614	$82.16	$82.15	$82.20
Purchase #5	$49.35	10.823%	$54.6912	$54.69	$54.70	$54.70
Purchase #6	$218.35	11.650%	$243.7878	$243.79	$243.80	$243.80
Purchase #7	$59.69	8.299%	$64.6437	$64.64	$64.65	$64.60
7 purchase totals =	$582.13		$643.0654	$643.06	$643.10	$643.00