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	$246.88	6.485%	$262.8902	$262.89	$262.90	$262.90
Purchase #2	$76.54	11.274%	$85.1691	$85.17	$85.15	$85.20
Purchase #3	$219.84	3.265%	$227.0178	$227.02	$227.00	$227.00
Purchase #4	$133.73	6.419%	$142.3141	$142.31	$142.30	$142.30
Purchase #5	$145.58	7.731%	$156.8348	$156.83	$156.85	$156.80
Purchase #6	$192.86	8.654%	$209.5501	$209.55	$209.55	$209.60
Purchase #7	$188.55	13.141%	$213.3274	$213.33	$213.35	$213.30
7 purchase totals =	$1,203.98		$1,297.1035	$1,297.10	$1,297.10	$1,297.10