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	$101.26	6.298%	$107.6374	$107.64	$107.65	$107.60
Purchase #2	$172.40	8.125%	$186.4075	$186.41	$186.40	$186.40
Purchase #3	$139.75	9.164%	$152.5567	$152.56	$152.55	$152.60
Purchase #4	$18.43	10.464%	$20.3585	$20.36	$20.35	$20.40
Purchase #5	$169.66	9.317%	$185.4672	$185.47	$185.45	$185.50
Purchase #6	$98.88	11.113%	$109.8685	$109.87	$109.85	$109.90
Purchase #7	$76.77	8.146%	$83.0237	$83.02	$83.00	$83.00
7 purchase totals =	$777.15		$845.3195	$845.33	$845.25	$845.40