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	$186.52	12.418%	$209.6821	$209.68	$209.70	$209.70
Purchase #2	$138.97	6.218%	$147.6112	$147.61	$147.60	$147.60
Purchase #3	$168.94	9.607%	$185.1701	$185.17	$185.15	$185.20
Purchase #4	$61.75	8.680%	$67.1099	$67.11	$67.10	$67.10
Purchase #5	$84.92	5.294%	$89.4157	$89.42	$89.40	$89.40
Purchase #6	$5.35	6.566%	$5.7013	$5.70	$5.70	$5.70
Purchase #7	$77.37	6.148%	$82.1267	$82.13	$82.15	$82.10
7 purchase totals =	$723.82		$786.8170	$786.82	$786.80	$786.80