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	$91.32	8.704%	$99.2685	$99.27	$99.25	$99.30
Purchase #2	$209.40	5.258%	$220.4103	$220.41	$220.40	$220.40
Purchase #3	$135.30	12.687%	$152.4655	$152.47	$152.45	$152.50
Purchase #4	$142.41	11.731%	$159.1161	$159.12	$159.10	$159.10
Purchase #5	$75.83	9.419%	$82.9724	$82.97	$82.95	$83.00
Purchase #6	$28.31	5.591%	$29.8928	$29.89	$29.90	$29.90
Purchase #7	$105.43	8.406%	$114.2924	$114.29	$114.30	$114.30
7 purchase totals =	$788.00		$858.4180	$858.42	$858.35	$858.50