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	$100.76	8.839%	$109.6662	$109.67	$109.65	$109.70
Purchase #2	$243.97	13.472%	$276.8376	$276.84	$276.85	$276.80
Purchase #3	$137.75	13.658%	$156.5639	$156.56	$156.55	$156.60
Purchase #4	$151.43	12.236%	$169.959	$169.96	$169.95	$170.00
Purchase #5	$10.61	10.339%	$11.707	$11.71	$11.70	$11.70
Purchase #6	$99.65	3.755%	$103.3919	$103.39	$103.40	$103.40
Purchase #7	$156.46	11.701%	$174.7674	$174.77	$174.75	$174.80
7 purchase totals =	$900.63		$1,002.8930	$1,002.90	$1,002.85	$1,003.00