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	$90.77	8.661%	$98.6316	$98.63	$98.65	$98.60
Purchase #2	$166.75	13.546%	$189.338	$189.34	$189.35	$189.30
Purchase #3	$137.76	3.431%	$142.4865	$142.49	$142.50	$142.50
Purchase #4	$124.55	3.452%	$128.8495	$128.85	$128.85	$128.80
Purchase #5	$118.75	12.732%	$133.8693	$133.87	$133.85	$133.90
Purchase #6	$146.94	12.244%	$164.9313	$164.93	$164.95	$164.90
Purchase #7	$141.72	9.674%	$155.43	$155.43	$155.45	$155.40
7 purchase totals =	$927.24		$1,013.5362	$1,013.54	$1,013.60	$1,013.40