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	$27.35	13.595%	$31.0682	$31.07	$31.05	$31.10
Purchase #2	$104.48	9.726%	$114.6417	$114.64	$114.65	$114.60
Purchase #3	$91.38	5.144%	$96.0806	$96.08	$96.10	$96.10
Purchase #4	$105.65	8.227%	$114.3418	$114.34	$114.35	$114.30
Purchase #5	$29.27	7.304%	$31.4079	$31.41	$31.40	$31.40
Purchase #6	$47.34	9.685%	$51.9249	$51.92	$51.90	$51.90
Purchase #7	$197.47	13.374%	$223.8796	$223.88	$223.90	$223.90
7 purchase totals =	$602.94		$663.3447	$663.34	$663.35	$663.30