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	$127.44	6.736%	$136.0244	$136.02	$136.00	$136.00
Purchase #2	$126.31	9.109%	$137.8156	$137.82	$137.80	$137.80
Purchase #3	$48.46	8.458%	$52.5587	$52.56	$52.55	$52.60
Purchase #4	$174.63	12.617%	$196.6631	$196.66	$196.65	$196.70
Purchase #5	$99.64	5.419%	$105.0395	$105.04	$105.05	$105.00
Purchase #6	$58.75	4.383%	$61.325	$61.33	$61.35	$61.30
Purchase #7	$198.69	12.554%	$223.6335	$223.63	$223.65	$223.60
7 purchase totals =	$833.92		$913.0598	$913.06	$913.05	$913.00