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	$100.62	9.230%	$109.9072	$109.91	$109.90	$109.90
Purchase #2	$249.30	5.339%	$262.6101	$262.61	$262.60	$262.60
Purchase #3	$236.41	7.781%	$254.8051	$254.81	$254.80	$254.80
Purchase #4	$170.54	7.273%	$182.9434	$182.94	$182.95	$182.90
Purchase #5	$130.45	6.839%	$139.3715	$139.37	$139.35	$139.40
Purchase #6	$81.79	11.388%	$91.1042	$91.10	$91.10	$91.10
Purchase #7	$58.37	11.386%	$65.016	$65.02	$65.00	$65.00
7 purchase totals =	$1,027.48		$1,105.7575	$1,105.76	$1,105.70	$1,105.70