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	$234.44	6.790%	$250.3585	$250.36	$250.35	$250.40
Purchase #2	$233.62	8.443%	$253.3445	$253.34	$253.35	$253.30
Purchase #3	$101.84	9.469%	$111.4832	$111.48	$111.50	$111.50
Purchase #4	$19.64	4.432%	$20.5104	$20.51	$20.50	$20.50
Purchase #5	$245.99	6.185%	$261.2045	$261.20	$261.20	$261.20
Purchase #6	$40.47	12.551%	$45.5494	$45.55	$45.55	$45.50
Purchase #7	$142.27	3.351%	$147.0375	$147.04	$147.05	$147.00
7 purchase totals =	$1,018.27		$1,089.4880	$1,089.48	$1,089.50	$1,089.40