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	$7.85	3.272%	$8.1069	$8.11	$8.10	$8.10
Purchase #2	$187.40	4.846%	$196.4814	$196.48	$196.50	$196.50
Purchase #3	$58.36	11.814%	$65.2547	$65.25	$65.25	$65.30
Purchase #4	$140.48	12.244%	$157.6804	$157.68	$157.70	$157.70
Purchase #5	$13.50	10.709%	$14.9457	$14.95	$14.95	$14.90
Purchase #6	$165.79	3.202%	$171.0986	$171.10	$171.10	$171.10
Purchase #7	$52.83	6.608%	$56.321	$56.32	$56.30	$56.30
7 purchase totals =	$626.21		$669.8887	$669.89	$669.90	$669.90