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	$81.32	12.256%	$91.2866	$91.29	$91.30	$91.30
Purchase #2	$213.71	3.541%	$221.2775	$221.28	$221.30	$221.30
Purchase #3	$222.69	12.396%	$250.2947	$250.29	$250.30	$250.30
Purchase #4	$178.67	9.389%	$195.4453	$195.45	$195.45	$195.40
Purchase #5	$208.33	13.208%	$235.8462	$235.85	$235.85	$235.80
Purchase #6	$29.55	11.651%	$32.9929	$32.99	$33.00	$33.00
Purchase #7	$19.73	7.791%	$21.2672	$21.27	$21.25	$21.30
7 purchase totals =	$954.00		$1,048.4104	$1,048.42	$1,048.45	$1,048.40