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	$114.91	8.279%	$124.4234	$124.42	$124.40	$124.40
Purchase #2	$144.73	7.831%	$156.0638	$156.06	$156.05	$156.10
Purchase #3	$183.25	11.804%	$204.8808	$204.88	$204.90	$204.90
Purchase #4	$189.59	12.571%	$213.4234	$213.42	$213.40	$213.40
Purchase #5	$97.76	7.499%	$105.091	$105.09	$105.10	$105.10
Purchase #6	$140.39	11.352%	$156.3271	$156.33	$156.35	$156.30
Purchase #7	$37.43	8.424%	$40.5831	$40.58	$40.60	$40.60
7 purchase totals =	$908.06		$1,000.7926	$1,000.78	$1,000.80	$1,000.80