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	$125.72	11.183%	$139.7793	$139.78	$139.80	$139.80
Purchase #2	$233.89	3.860%	$242.9182	$242.92	$242.90	$242.90
Purchase #3	$154.94	11.339%	$172.5086	$172.51	$172.50	$172.50
Purchase #4	$207.27	6.524%	$220.7923	$220.79	$220.80	$220.80
Purchase #5	$89.80	11.115%	$99.7813	$99.78	$99.80	$99.80
Purchase #6	$180.80	9.418%	$197.8277	$197.83	$197.85	$197.80
Purchase #7	$35.85	4.153%	$37.3389	$37.34	$37.35	$37.30
7 purchase totals =	$1,028.27		$1,110.9463	$1,110.95	$1,111.00	$1,110.90