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	$97.54	5.687%	$103.0871	$103.09	$103.10	$103.10
Purchase #2	$168.54	6.330%	$179.2086	$179.21	$179.20	$179.20
Purchase #3	$225.45	5.834%	$238.6028	$238.60	$238.60	$238.60
Purchase #4	$213.54	8.598%	$231.9002	$231.90	$231.90	$231.90
Purchase #5	$185.63	9.850%	$203.9146	$203.91	$203.90	$203.90
Purchase #6	$131.79	10.404%	$145.5014	$145.50	$145.50	$145.50
Purchase #7	$48.60	11.150%	$54.0189	$54.02	$54.00	$54.00
7 purchase totals =	$1,071.09		$1,156.2336	$1,156.23	$1,156.20	$1,156.20