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	$28.41	10.447%	$31.378	$31.38	$31.40	$31.40
Purchase #2	$58.26	12.149%	$65.338	$65.34	$65.35	$65.30
Purchase #3	$101.84	4.590%	$106.5145	$106.51	$106.50	$106.50
Purchase #4	$236.70	8.227%	$256.1733	$256.17	$256.15	$256.20
Purchase #5	$54.43	12.701%	$61.3432	$61.34	$61.35	$61.30
Purchase #6	$80.83	5.592%	$85.35	$85.35	$85.35	$85.40
Purchase #7	$73.64	3.762%	$76.4103	$76.41	$76.40	$76.40
7 purchase totals =	$634.11		$682.5073	$682.50	$682.50	$682.50