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	$36.79	6.229%	$39.0816	$39.08	$39.10	$39.10
Purchase #2	$235.39	8.871%	$256.2714	$256.27	$256.25	$256.30
Purchase #3	$91.54	6.700%	$97.6732	$97.67	$97.65	$97.70
Purchase #4	$96.32	7.494%	$103.5382	$103.54	$103.55	$103.50
Purchase #5	$55.63	11.625%	$62.097	$62.10	$62.10	$62.10
Purchase #6	$77.89	5.441%	$82.128	$82.13	$82.15	$82.10
Purchase #7	$181.86	3.294%	$187.8505	$187.85	$187.85	$187.90
7 purchase totals =	$775.42		$828.6399	$828.64	$828.65	$828.70