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	$135.81	13.784%	$154.5301	$154.53	$154.55	$154.50
Purchase #2	$158.53	10.610%	$175.35	$175.35	$175.35	$175.40
Purchase #3	$191.50	12.639%	$215.7037	$215.70	$215.70	$215.70
Purchase #4	$162.64	6.221%	$172.7578	$172.76	$172.75	$172.80
Purchase #5	$186.38	13.375%	$211.3083	$211.31	$211.30	$211.30
Purchase #6	$43.30	10.414%	$47.8093	$47.81	$47.80	$47.80
Purchase #7	$162.68	6.265%	$172.8719	$172.87	$172.85	$172.90
7 purchase totals =	$1,040.84		$1,150.3311	$1,150.33	$1,150.30	$1,150.40