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	$234.70	12.331%	$263.6409	$263.64	$263.65	$263.60
Purchase #2	$176.63	6.732%	$188.5207	$188.52	$188.50	$188.50
Purchase #3	$67.33	5.367%	$70.9436	$70.94	$70.95	$70.90
Purchase #4	$125.86	13.695%	$143.0965	$143.10	$143.10	$143.10
Purchase #5	$85.81	3.787%	$89.0596	$89.06	$89.05	$89.10
Purchase #6	$198.63	12.478%	$223.4151	$223.42	$223.40	$223.40
Purchase #7	$103.78	9.292%	$113.4232	$113.42	$113.40	$113.40
7 purchase totals =	$992.74		$1,092.0996	$1,092.10	$1,092.05	$1,092.00