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	$171.55	9.518%	$187.8781	$187.88	$187.90	$187.90
Purchase #2	$80.54	13.629%	$91.5168	$91.52	$91.50	$91.50
Purchase #3	$229.47	12.225%	$257.5227	$257.52	$257.50	$257.50
Purchase #4	$236.73	6.398%	$251.876	$251.88	$251.90	$251.90
Purchase #5	$75.71	7.386%	$81.3019	$81.30	$81.30	$81.30
Purchase #6	$121.52	4.822%	$127.3797	$127.38	$127.40	$127.40
Purchase #7	$169.74	12.254%	$190.5399	$190.54	$190.55	$190.50
7 purchase totals =	$1,085.26		$1,188.0151	$1,188.02	$1,188.05	$1,188.00