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	$126.91	3.539%	$131.4013	$131.40	$131.40	$131.40
Purchase #2	$37.68	10.240%	$41.5384	$41.54	$41.55	$41.50
Purchase #3	$112.31	12.647%	$126.5138	$126.51	$126.50	$126.50
Purchase #4	$238.59	7.112%	$255.5585	$255.56	$255.55	$255.60
Purchase #5	$77.35	6.500%	$82.3778	$82.38	$82.40	$82.40
Purchase #6	$7.74	12.214%	$8.6854	$8.69	$8.70	$8.70
Purchase #7	$172.77	3.172%	$178.2503	$178.25	$178.25	$178.30
7 purchase totals =	$773.35		$824.3255	$824.33	$824.35	$824.40