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	$56.75	5.360%	$59.7918	$59.79	$59.80	$59.80
Purchase #2	$82.33	3.365%	$85.1004	$85.10	$85.10	$85.10
Purchase #3	$31.69	11.728%	$35.4066	$35.41	$35.40	$35.40
Purchase #4	$139.56	11.705%	$155.8955	$155.90	$155.90	$155.90
Purchase #5	$13.95	6.696%	$14.8841	$14.88	$14.90	$14.90
Purchase #6	$130.37	4.431%	$136.1467	$136.15	$136.15	$136.10
Purchase #7	$70.54	12.842%	$79.5987	$79.60	$79.60	$79.60
7 purchase totals =	$525.19		$566.8238	$566.83	$566.85	$566.80