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	$29.85	13.463%	$33.8687	$33.87	$33.85	$33.90
Purchase #2	$177.52	12.816%	$200.271	$200.27	$200.25	$200.30
Purchase #3	$50.51	7.519%	$54.3078	$54.31	$54.30	$54.30
Purchase #4	$238.91	12.764%	$269.4045	$269.40	$269.40	$269.40
Purchase #5	$194.98	5.662%	$206.0198	$206.02	$206.00	$206.00
Purchase #6	$92.88	11.481%	$103.5436	$103.54	$103.55	$103.50
Purchase #7	$198.94	5.216%	$209.3167	$209.32	$209.30	$209.30
7 purchase totals =	$983.59		$1,076.7321	$1,076.73	$1,076.65	$1,076.70