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	$79.66	3.169%	$82.1844	$82.18	$82.20	$82.20
Purchase #2	$73.95	10.212%	$81.5018	$81.50	$81.50	$81.50
Purchase #3	$102.88	6.715%	$109.7884	$109.79	$109.80	$109.80
Purchase #4	$73.59	6.371%	$78.2784	$78.28	$78.30	$78.30
Purchase #5	$76.69	12.734%	$86.4557	$86.46	$86.45	$86.50
Purchase #6	$42.99	6.511%	$45.7891	$45.79	$45.80	$45.80
Purchase #7	$48.35	3.421%	$50.0041	$50.00	$50.00	$50.00
7 purchase totals =	$498.11		$534.0019	$534.00	$534.05	$534.10