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	$188.39	12.308%	$211.577	$211.58	$211.60	$211.60
Purchase #2	$65.60	10.579%	$72.5398	$72.54	$72.55	$72.50
Purchase #3	$90.90	10.644%	$100.5754	$100.58	$100.60	$100.60
Purchase #4	$68.59	6.764%	$73.2294	$73.23	$73.25	$73.20
Purchase #5	$234.55	9.271%	$256.2951	$256.30	$256.30	$256.30
Purchase #6	$82.90	10.131%	$91.2986	$91.30	$91.30	$91.30
Purchase #7	$47.70	8.120%	$51.5732	$51.57	$51.55	$51.60
7 purchase totals =	$778.63		$857.0885	$857.10	$857.15	$857.10