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	$50.98	8.494%	$55.3102	$55.31	$55.30	$55.30
Purchase #2	$176.31	5.251%	$185.568	$185.57	$185.55	$185.60
Purchase #3	$158.47	11.744%	$177.0807	$177.08	$177.10	$177.10
Purchase #4	$170.58	8.651%	$185.3369	$185.34	$185.35	$185.30
Purchase #5	$168.94	9.759%	$185.4269	$185.43	$185.45	$185.40
Purchase #6	$145.57	9.554%	$159.4778	$159.48	$159.50	$159.50
Purchase #7	$49.47	4.582%	$51.7367	$51.74	$51.75	$51.70
7 purchase totals =	$920.32		$999.9372	$999.95	$1,000.00	$999.90