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	$243.74	4.813%	$255.4712	$255.47	$255.45	$255.50
Purchase #2	$176.88	8.503%	$191.9201	$191.92	$191.90	$191.90
Purchase #3	$235.43	8.412%	$255.2344	$255.23	$255.25	$255.20
Purchase #4	$201.38	5.780%	$213.0198	$213.02	$213.00	$213.00
Purchase #5	$176.92	12.354%	$198.7767	$198.78	$198.80	$198.80
Purchase #6	$41.50	5.670%	$43.8531	$43.85	$43.85	$43.90
Purchase #7	$236.35	11.462%	$263.4404	$263.44	$263.45	$263.40
7 purchase totals =	$1,312.20		$1,421.7157	$1,421.71	$1,421.70	$1,421.70