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	$110.83	13.832%	$126.16	$126.16	$126.15	$126.20
Purchase #2	$249.72	13.497%	$283.4247	$283.42	$283.40	$283.40
Purchase #3	$39.45	6.180%	$41.888	$41.89	$41.90	$41.90
Purchase #4	$164.32	8.488%	$178.2675	$178.27	$178.25	$178.30
Purchase #5	$243.45	7.143%	$260.8396	$260.84	$260.85	$260.80
Purchase #6	$169.28	9.510%	$185.3785	$185.38	$185.40	$185.40
Purchase #7	$50.83	8.497%	$55.149	$55.15	$55.15	$55.10
7 purchase totals =	$1,027.88		$1,131.1073	$1,131.11	$1,131.10	$1,131.10