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	$85.97	4.419%	$89.769	$89.77	$89.75	$89.80
Purchase #2	$209.66	13.522%	$238.0102	$238.01	$238.00	$238.00
Purchase #3	$124.31	5.816%	$131.5399	$131.54	$131.55	$131.50
Purchase #4	$78.39	8.821%	$85.3048	$85.30	$85.30	$85.30
Purchase #5	$162.30	12.209%	$182.1152	$182.12	$182.10	$182.10
Purchase #6	$149.84	12.713%	$168.8892	$168.89	$168.90	$168.90
Purchase #7	$9.47	6.435%	$10.0794	$10.08	$10.10	$10.10
7 purchase totals =	$819.94		$905.7077	$905.71	$905.70	$905.70