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	$17.56	7.735%	$18.9183	$18.92	$18.90	$18.90
Purchase #2	$80.81	3.667%	$83.7733	$83.77	$83.75	$83.80
Purchase #3	$229.48	7.582%	$246.8792	$246.88	$246.90	$246.90
Purchase #4	$175.94	10.584%	$194.5615	$194.56	$194.55	$194.60
Purchase #5	$111.55	13.329%	$126.4185	$126.42	$126.40	$126.40
Purchase #6	$128.46	5.781%	$135.8863	$135.89	$135.90	$135.90
Purchase #7	$218.59	11.435%	$243.5858	$243.59	$243.60	$243.60
7 purchase totals =	$962.39		$1,050.0229	$1,050.03	$1,050.00	$1,050.10