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	$238.46	6.202%	$253.2493	$253.25	$253.25	$253.20
Purchase #2	$187.92	13.851%	$213.9488	$213.95	$213.95	$213.90
Purchase #3	$152.64	10.421%	$168.5466	$168.55	$168.55	$168.50
Purchase #4	$50.94	10.395%	$56.2352	$56.24	$56.25	$56.20
Purchase #5	$174.86	5.403%	$184.3077	$184.31	$184.30	$184.30
Purchase #6	$83.44	7.228%	$89.471	$89.47	$89.45	$89.50
Purchase #7	$85.35	8.585%	$92.6773	$92.68	$92.70	$92.70
7 purchase totals =	$973.61		$1,058.4359	$1,058.45	$1,058.45	$1,058.30