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	$168.38	10.334%	$185.7804	$185.78	$185.80	$185.80
Purchase #2	$212.38	13.142%	$240.291	$240.29	$240.30	$240.30
Purchase #3	$123.39	11.474%	$137.5478	$137.55	$137.55	$137.50
Purchase #4	$67.52	11.645%	$75.3827	$75.38	$75.40	$75.40
Purchase #5	$189.52	5.573%	$200.0819	$200.08	$200.10	$200.10
Purchase #6	$29.84	10.664%	$33.0221	$33.02	$33.00	$33.00
Purchase #7	$90.93	9.465%	$99.5365	$99.54	$99.55	$99.50
7 purchase totals =	$881.96		$971.6424	$971.64	$971.70	$971.60