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	$69.37	11.575%	$77.3996	$77.40	$77.40	$77.40
Purchase #2	$169.40	12.112%	$189.9177	$189.92	$189.90	$189.90
Purchase #3	$130.77	8.530%	$141.9247	$141.92	$141.90	$141.90
Purchase #4	$144.42	13.802%	$164.3528	$164.35	$164.35	$164.40
Purchase #5	$114.62	7.336%	$123.0285	$123.03	$123.05	$123.00
Purchase #6	$92.72	4.504%	$96.8961	$96.90	$96.90	$96.90
Purchase #7	$149.82	5.362%	$157.8533	$157.85	$157.85	$157.90
7 purchase totals =	$871.12		$951.3727	$951.37	$951.35	$951.40