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	$83.69	7.691%	$90.1266	$90.13	$90.15	$90.10
Purchase #2	$165.34	9.662%	$181.3152	$181.32	$181.30	$181.30
Purchase #3	$47.86	8.509%	$51.9324	$51.93	$51.95	$51.90
Purchase #4	$229.48	8.163%	$248.2125	$248.21	$248.20	$248.20
Purchase #5	$165.56	10.208%	$182.4604	$182.46	$182.45	$182.50
Purchase #6	$50.78	9.317%	$55.5112	$55.51	$55.50	$55.50
Purchase #7	$33.34	7.753%	$35.9249	$35.92	$35.90	$35.90
7 purchase totals =	$776.05		$845.4832	$845.48	$845.45	$845.40