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	$90.74	9.755%	$99.5917	$99.59	$99.60	$99.60
Purchase #2	$215.38	3.558%	$223.0432	$223.04	$223.05	$223.00
Purchase #3	$104.49	7.503%	$112.3299	$112.33	$112.35	$112.30
Purchase #4	$34.31	13.406%	$38.9096	$38.91	$38.90	$38.90
Purchase #5	$123.66	4.303%	$128.9811	$128.98	$129.00	$129.00
Purchase #6	$42.33	6.361%	$45.0226	$45.02	$45.00	$45.00
Purchase #7	$31.53	5.333%	$33.2115	$33.21	$33.20	$33.20
7 purchase totals =	$642.44		$681.0896	$681.08	$681.10	$681.00