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	$85.99	7.136%	$92.1262	$92.13	$92.15	$92.10
Purchase #2	$196.56	12.840%	$221.7983	$221.80	$221.80	$221.80
Purchase #3	$79.88	6.774%	$85.2911	$85.29	$85.30	$85.30
Purchase #4	$82.96	3.330%	$85.7226	$85.72	$85.70	$85.70
Purchase #5	$26.43	7.659%	$28.4543	$28.45	$28.45	$28.50
Purchase #6	$131.94	8.584%	$143.2657	$143.27	$143.25	$143.30
Purchase #7	$156.35	9.106%	$170.5872	$170.59	$170.60	$170.60
7 purchase totals =	$760.11		$827.2454	$827.25	$827.25	$827.30