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	$20.40	6.506%	$21.7272	$21.73	$21.75	$21.70
Purchase #2	$205.56	11.596%	$229.3967	$229.40	$229.40	$229.40
Purchase #3	$35.83	4.406%	$37.4087	$37.41	$37.40	$37.40
Purchase #4	$204.84	7.454%	$220.1088	$220.11	$220.10	$220.10
Purchase #5	$187.69	11.824%	$209.8825	$209.88	$209.90	$209.90
Purchase #6	$54.70	9.534%	$59.9151	$59.92	$59.90	$59.90
Purchase #7	$197.50	10.872%	$218.9722	$218.97	$218.95	$219.00
7 purchase totals =	$906.52		$997.4112	$997.42	$997.40	$997.40