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	$133.88	3.735%	$138.8804	$138.88	$138.90	$138.90
Purchase #2	$50.56	3.231%	$52.1936	$52.19	$52.20	$52.20
Purchase #3	$211.38	8.402%	$229.1401	$229.14	$229.15	$229.10
Purchase #4	$74.48	7.566%	$80.1152	$80.12	$80.10	$80.10
Purchase #5	$187.94	4.682%	$196.7394	$196.74	$196.75	$196.70
Purchase #6	$246.46	10.151%	$271.4782	$271.48	$271.50	$271.50
Purchase #7	$118.48	12.123%	$132.8433	$132.84	$132.85	$132.80
7 purchase totals =	$1,023.18		$1,101.3902	$1,101.39	$1,101.45	$1,101.30