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	$189.59	12.359%	$213.0214	$213.02	$213.00	$213.00
Purchase #2	$78.81	10.791%	$87.3144	$87.31	$87.30	$87.30
Purchase #3	$73.85	11.781%	$82.5503	$82.55	$82.55	$82.60
Purchase #4	$154.96	12.508%	$174.3424	$174.34	$174.35	$174.30
Purchase #5	$141.25	5.765%	$149.3931	$149.39	$149.40	$149.40
Purchase #6	$56.47	8.332%	$61.1751	$61.18	$61.20	$61.20
Purchase #7	$99.42	11.682%	$111.0342	$111.03	$111.05	$111.00
7 purchase totals =	$794.35		$878.8309	$878.82	$878.85	$878.80