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	$70.85	10.145%	$78.0377	$78.04	$78.05	$78.00
Purchase #2	$36.40	8.480%	$39.4867	$39.49	$39.50	$39.50
Purchase #3	$25.89	10.865%	$28.7029	$28.70	$28.70	$28.70
Purchase #4	$70.85	11.405%	$78.9304	$78.93	$78.95	$78.90
Purchase #5	$125.41	11.438%	$139.7544	$139.75	$139.75	$139.80
Purchase #6	$150.51	8.120%	$162.7314	$162.73	$162.75	$162.70
Purchase #7	$99.39	10.630%	$109.9552	$109.96	$109.95	$110.00
7 purchase totals =	$579.30		$637.5987	$637.60	$637.65	$637.60