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	$59.47	9.711%	$65.2451	$65.25	$65.25	$65.20
Purchase #2	$91.30	12.250%	$102.4843	$102.48	$102.50	$102.50
Purchase #3	$85.72	5.165%	$90.1474	$90.15	$90.15	$90.10
Purchase #4	$181.39	11.276%	$201.8435	$201.84	$201.85	$201.80
Purchase #5	$67.71	5.362%	$71.3406	$71.34	$71.35	$71.30
Purchase #6	$49.38	4.299%	$51.5028	$51.50	$51.50	$51.50
Purchase #7	$202.86	6.159%	$215.3541	$215.35	$215.35	$215.40
7 purchase totals =	$737.83		$797.9178	$797.91	$797.95	$797.80