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	$49.39	13.229%	$55.9238	$55.92	$55.90	$55.90
Purchase #2	$14.26	7.566%	$15.3389	$15.34	$15.35	$15.30
Purchase #3	$176.95	6.841%	$189.0551	$189.06	$189.05	$189.10
Purchase #4	$98.90	12.659%	$111.4198	$111.42	$111.40	$111.40
Purchase #5	$223.30	4.142%	$232.5491	$232.55	$232.55	$232.50
Purchase #6	$67.28	7.505%	$72.3294	$72.33	$72.35	$72.30
Purchase #7	$86.94	6.454%	$92.5511	$92.55	$92.55	$92.60
7 purchase totals =	$717.02		$769.1672	$769.17	$769.15	$769.10