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	$169.25	12.733%	$190.8006	$190.80	$190.80	$190.80
Purchase #2	$155.63	4.357%	$162.4108	$162.41	$162.40	$162.40
Purchase #3	$68.53	5.751%	$72.4712	$72.47	$72.45	$72.50
Purchase #4	$161.48	6.316%	$171.6791	$171.68	$171.70	$171.70
Purchase #5	$238.66	11.158%	$265.2897	$265.29	$265.30	$265.30
Purchase #6	$7.37	4.859%	$7.7281	$7.73	$7.75	$7.70
Purchase #7	$35.56	12.211%	$39.9022	$39.90	$39.90	$39.90
7 purchase totals =	$836.48		$910.2817	$910.28	$910.30	$910.30