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	$29.83	13.364%	$33.8165	$33.82	$33.80	$33.80
Purchase #2	$7.92	13.474%	$8.9871	$8.99	$9.00	$9.00
Purchase #3	$240.69	13.661%	$273.5707	$273.57	$273.55	$273.60
Purchase #4	$177.88	7.328%	$190.915	$190.92	$190.90	$190.90
Purchase #5	$54.63	8.498%	$59.2725	$59.27	$59.25	$59.30
Purchase #6	$101.26	9.833%	$111.2169	$111.22	$111.20	$111.20
Purchase #7	$209.33	4.278%	$218.2851	$218.29	$218.30	$218.30
7 purchase totals =	$821.54		$896.0638	$896.08	$896.00	$896.10