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	$73.46	5.330%	$77.3754	$77.38	$77.40	$77.40
Purchase #2	$58.35	7.738%	$62.8651	$62.87	$62.85	$62.90
Purchase #3	$39.39	3.279%	$40.6816	$40.68	$40.70	$40.70
Purchase #4	$51.39	7.550%	$55.2699	$55.27	$55.25	$55.30
Purchase #5	$95.61	9.811%	$104.9903	$104.99	$105.00	$105.00
Purchase #6	$45.94	12.159%	$51.5258	$51.53	$51.55	$51.50
Purchase #7	$92.54	3.791%	$96.0482	$96.05	$96.05	$96.00
7 purchase totals =	$456.68		$488.7563	$488.77	$488.80	$488.80