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	$189.47	10.359%	$209.0972	$209.10	$209.10	$209.10
Purchase #2	$249.29	6.209%	$264.7684	$264.77	$264.75	$264.80
Purchase #3	$31.30	11.498%	$34.8989	$34.90	$34.90	$34.90
Purchase #4	$30.47	4.682%	$31.8966	$31.90	$31.90	$31.90
Purchase #5	$112.66	11.489%	$125.6035	$125.60	$125.60	$125.60
Purchase #6	$200.56	11.321%	$223.2654	$223.27	$223.25	$223.30
Purchase #7	$19.66	5.737%	$20.7879	$20.79	$20.80	$20.80
7 purchase totals =	$833.41		$910.3179	$910.33	$910.30	$910.40