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	$178.31	7.476%	$191.6405	$191.64	$191.65	$191.60
Purchase #2	$123.67	6.289%	$131.4476	$131.45	$131.45	$131.40
Purchase #3	$99.93	8.667%	$108.5909	$108.59	$108.60	$108.60
Purchase #4	$196.32	5.409%	$206.9389	$206.94	$206.95	$206.90
Purchase #5	$192.89	10.653%	$213.4386	$213.44	$213.45	$213.40
Purchase #6	$7.74	11.818%	$8.6547	$8.65	$8.65	$8.70
Purchase #7	$81.72	9.347%	$89.3584	$89.36	$89.35	$89.40
7 purchase totals =	$880.58		$950.0696	$950.07	$950.10	$950.00