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	$137.65	5.641%	$145.4148	$145.41	$145.40	$145.40
Purchase #2	$126.80	13.604%	$144.0499	$144.05	$144.05	$144.00
Purchase #3	$89.62	12.851%	$101.1371	$101.14	$101.15	$101.10
Purchase #4	$117.59	7.508%	$126.4187	$126.42	$126.40	$126.40
Purchase #5	$91.79	12.260%	$103.0435	$103.04	$103.05	$103.00
Purchase #6	$28.83	8.802%	$31.3676	$31.37	$31.35	$31.40
Purchase #7	$36.29	4.666%	$37.9833	$37.98	$38.00	$38.00
7 purchase totals =	$628.57		$689.4149	$689.41	$689.40	$689.30